[cleanup] examples test_run_squad uses tiny model
Author: sshleifer
Pull request: yes

This speeds up the examples tests from 120s to 70s.
Note that this probably understates the difference, since all the relevant models are cached on my local machine.
We can also improve `test_run_glue` in a future PR.
I made an issue discussing improvements this PR does not fix: #5059 


### More detail:

Before (master):  119.36s


```bash
============================ slowest test durations ============================
42.69s call     examples/test_examples.py::ExamplesTests::test_run_squad
21.20s call     examples/test_examples.py::ExamplesTests::test_run_glue
19.02s call     examples/token-classification/test_ner_examples.py::ExamplesTests::test_run_ner
13.65s call     examples/test_examples.py::ExamplesTests::test_run_language_modeling
3.80s call     examples/test_examples.py::ExamplesTests::test_generation

```
After: 69.3 Seconds
```bash
============================ slowest test durations ============================
19.12s call     examples/token-classification/test_ner_examples.py::ExamplesTests::test_run_ner
14.60s call     examples/test_examples.py::ExamplesTests::test_run_language_modeling
13.49s call     examples/test_examples.py::ExamplesTests::test_run_glue
3.87s call     examples/summarization/test_summarization_examples.py::TestBartExamples::test_bart_run_sum_cli
3.08s call     examples/translation/t5/test_t5_examples.py::TestT5Examples::test_t5_cli
2.64s call     examples/summarization/test_summarization_examples.py::TestT5Examples::test_t5_cli
2.20s call     examples/summarization/test_summarization_examples.py::TestBartExamples::test_t5_run_sum_cli
1.81s call     examples/test_examples.py::ExamplesTests::test_run_squad
1.67s call     examples/test_examples.py::ExamplesTests::test_generation

```


Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5059?src=pr&el=h1) Report
> Merging [#5059](https://codecov.io/gh/huggingface/transformers/pull/5059?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/d5477baf7d87b9bdad386f2f317732b85277b06b&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/5059/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/5059?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #5059   +/-   ##
=======================================
  Coverage   77.41%   77.41%           
=======================================
  Files         130      130           
  Lines       22023    22023           
=======================================
  Hits        17050    17050           
  Misses       4973     4973           
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/5059?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5059/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `75.00% <0.00%> (-0.41%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5059/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `87.42% <0.00%> (+0.15%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/5059?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5059?src=pr&el=footer). Last update [d5477ba...6bef869](https://codecov.io/gh/huggingface/transformers/pull/5059?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).


Merging so that external contrib can pick up the next steps without conflicts. Feel free to add comments here or in #5057