[WIP][FIX] Prevent output some config files when using fast tokenizer
Author: europeanplaice
Pull request: yes

# What does this PR do?

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Fixes #12308
One of the candidates of this issue's cause is the crash of configurations of fast tokenizer and tokenizer.
With fast tokenizer, `tokenizer.json` do all things and `special_tokens_map.json` and `tokenizer_config.json` are not needed.
When using fast tokenizer, this PR avoids output the two files.

This is a quick fix and I have not written test and checked the effects of this code on other programs.
I'd like to receive your reviews and criticism.


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Comments:
Hello! Does this resolve #12308?

Hello!
Sorry if I may have been unclear.
Assuming the difference between `spm.SentencePieceTrainer` and `ReformerTokenizerFast` is anticipated, this PR tentatively resolve the difference between `ReformerTokenizerFast` and `AutoTokenizer.from_pretrained('test')`.

Output is below.
```
 sentencepiece  9: ['L', 'o', '<mask>', 'm▁', 'I', 'p', 's', 'um', '▁']
  transformers 10: ['▁', 'L', 'o', '<mask>', 'm', '▁', 'I', 'p', 's', 'um']
 AutoTokenizer 10: ['▁', 'L', 'o', '<mask>', 'm', '▁', 'I', 'p', 's', 'um']
```

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