Remove dead code for non-dict data_files from packaged modules

Remove dead code for non-dict data_files from packaged modules.

Since the merge of this PR:
- #2986

the builders' variable self.config.data_files is always a dict, which makes the condition on (str, list, tuple) dead code.

Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6911). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.005136 / 0.011353 (-0.006217) | 0.003136 / 0.011008 (-0.007872) | 0.063752 / 0.038508 (0.025244) | 0.031060 / 0.023109 (0.007950) | 0.249848 / 0.275898 (-0.026050) | 0.275918 / 0.323480 (-0.047561) | 0.004047 / 0.007986 (-0.003938) | 0.002696 / 0.004328 (-0.001632) | 0.049884 / 0.004250 (0.045634) | 0.044646 / 0.037052 (0.007593) | 0.264769 / 0.258489 (0.006280) | 0.299874 / 0.293841 (0.006033) | 0.027530 / 0.128546 (-0.101016) | 0.010026 / 0.075646 (-0.065620) | 0.204007 / 0.419271 (-0.215265) | 0.035982 / 0.043533 (-0.007550) | 0.253560 / 0.255139 (-0.001579) | 0.276206 / 0.283200 (-0.006993) | 0.017770 / 0.141683 (-0.123913) | 1.156008 / 1.452155 (-0.296146) | 1.197265 / 1.492716 (-0.295451) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.092960 / 0.018006 (0.074954) | 0.302876 / 0.000490 (0.302386) | 0.000214 / 0.000200 (0.000014) | 0.000044 / 0.000054 (-0.000010) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.019060 / 0.037411 (-0.018351) | 0.062262 / 0.014526 (0.047737) | 0.073836 / 0.176557 (-0.102721) | 0.122327 / 0.737135 (-0.614809) | 0.076050 / 0.296338 (-0.220289) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.282489 / 0.215209 (0.067280) | 2.745084 / 2.077655 (0.667429) | 1.453044 / 1.504120 (-0.051076) | 1.339065 / 1.541195 (-0.202130) | 1.341395 / 1.468490 (-0.127095) | 0.586497 / 4.584777 (-3.998280) | 2.342198 / 3.745712 (-1.403514) | 2.684984 / 5.269862 (-2.584878) | 1.703738 / 4.565676 (-2.861939) | 0.062489 / 0.424275 (-0.361786) | 0.004906 / 0.007607 (-0.002701) | 0.332325 / 0.226044 (0.106280) | 3.255381 / 2.268929 (0.986452) | 1.797045 / 55.444624 (-53.647579) | 1.515197 / 6.876477 (-5.361280) | 1.508317 / 2.142072 (-0.633756) | 0.635973 / 4.805227 (-4.169254) | 0.117292 / 6.500664 (-6.383372) | 0.041456 / 0.075469 (-0.034013) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.973934 / 1.841788 (-0.867853) | 11.288665 / 8.074308 (3.214356) | 9.269404 / 10.191392 (-0.921988) | 0.143190 / 0.680424 (-0.537234) | 0.014366 / 0.534201 (-0.519835) | 0.285936 / 0.579283 (-0.293347) | 0.261632 / 0.434364 (-0.172732) | 0.327191 / 0.540337 (-0.213146) | 0.418900 / 1.386936 (-0.968036) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.005131 / 0.011353 (-0.006222) | 0.003181 / 0.011008 (-0.007827) | 0.049697 / 0.038508 (0.011189) | 0.032754 / 0.023109 (0.009645) | 0.263954 / 0.275898 (-0.011944) | 0.285110 / 0.323480 (-0.038370) | 0.004133 / 0.007986 (-0.003852) | 0.002713 / 0.004328 (-0.001615) | 0.051684 / 0.004250 (0.047433) | 0.040607 / 0.037052 (0.003554) | 0.277919 / 0.258489 (0.019429) | 0.304773 / 0.293841 (0.010932) | 0.029530 / 0.128546 (-0.099016) | 0.010176 / 0.075646 (-0.065470) | 0.058501 / 0.419271 (-0.360771) | 0.033436 / 0.043533 (-0.010097) | 0.269899 / 0.255139 (0.014760) | 0.284490 / 0.283200 (0.001290) | 0.017092 / 0.141683 (-0.124591) | 1.132399 / 1.452155 (-0.319756) | 1.167290 / 1.492716 (-0.325427) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.094460 / 0.018006 (0.076454) | 0.301462 / 0.000490 (0.300972) | 0.000202 / 0.000200 (0.000002) | 0.000052 / 0.000054 (-0.000003) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.022767 / 0.037411 (-0.014645) | 0.075993 / 0.014526 (0.061467) | 0.087729 / 0.176557 (-0.088827) | 0.127599 / 0.737135 (-0.609536) | 0.088873 / 0.296338 (-0.207465) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.286420 / 0.215209 (0.071211) | 2.811376 / 2.077655 (0.733722) | 1.558645 / 1.504120 (0.054525) | 1.426371 / 1.541195 (-0.114824) | 1.422347 / 1.468490 (-0.046143) | 0.567181 / 4.584777 (-4.017596) | 0.936731 / 3.745712 (-2.808982) | 2.643566 / 5.269862 (-2.626296) | 1.727843 / 4.565676 (-2.837834) | 0.062748 / 0.424275 (-0.361527) | 0.005033 / 0.007607 (-0.002574) | 0.339708 / 0.226044 (0.113663) | 3.354119 / 2.268929 (1.085190) | 1.877594 / 55.444624 (-53.567030) | 1.589202 / 6.876477 (-5.287274) | 1.707780 / 2.142072 (-0.434292) | 0.644520 / 4.805227 (-4.160708) | 0.115226 / 6.500664 (-6.385438) | 0.040004 / 0.075469 (-0.035465) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.002774 / 1.841788 (-0.839014) | 11.812647 / 8.074308 (3.738339) | 10.384198 / 10.191392 (0.192806) | 0.131120 / 0.680424 (-0.549304) | 0.014862 / 0.534201 (-0.519339) | 0.282873 / 0.579283 (-0.296410) | 0.120415 / 0.434364 (-0.313949) | 0.321995 / 0.540337 (-0.218343) | 0.441987 / 1.386936 (-0.944949) |

</details>
</details>

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