Remove pytest dependency.
This is a follow-up to PR #2055. This file was added between the moment I wrote #2055 and the moment in was merged.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2093?src=pr&el=h1) Report
> Merging [#2093](https://codecov.io/gh/huggingface/transformers/pull/2093?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/2670b0d682746e1fe94ab9c7b4d2fd7f4af03193?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2093/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2093?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #2093      +/-   ##
==========================================
- Coverage   82.67%   82.65%   -0.02%     
==========================================
  Files         111      111              
  Lines       16162    16162              
==========================================
- Hits        13362    13359       -3     
- Misses       2800     2803       +3
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2093?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/tests/optimization\_tf\_test.py](https://codecov.io/gh/huggingface/transformers/pull/2093/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL29wdGltaXphdGlvbl90Zl90ZXN0LnB5) | `86.76% <100%> (ø)` | :arrow_up: |
| [transformers/tests/modeling\_tf\_common\_test.py](https://codecov.io/gh/huggingface/transformers/pull/2093/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL21vZGVsaW5nX3RmX2NvbW1vbl90ZXN0LnB5) | `95.38% <0%> (-1.54%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/2093?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/2093?src=pr&el=footer). Last update [2670b0d...010489c](https://codecov.io/gh/huggingface/transformers/pull/2093?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>@julien-c Could you merge this please? :-)