Remove jitted method so that our models are pickable.
closes https://github.com/huggingface/transformers/issues/4038
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4050?src=pr&el=h1) Report
> Merging [#4050](https://codecov.io/gh/huggingface/transformers/pull/4050?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/9a0a8c1c6f4f2f0c80ff07d36713a3ada785eec5&el=desc) will **increase** coverage by `0.00%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4050/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4050?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #4050   +/-   ##
=======================================
  Coverage   78.87%   78.88%           
=======================================
  Files         111      111           
  Lines       18536    18533    -3     
=======================================
- Hits        14621    14620    -1     
+ Misses       3915     3913    -2     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4050?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/activations.py](https://codecov.io/gh/huggingface/transformers/pull/4050/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9hY3RpdmF0aW9ucy5weQ==) | `88.88% <ø> (+7.93%)` | :arrow_up: |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4050/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `73.02% <0.00%> (ø)` | |

------

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> **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/4050?src=pr&el=footer). Last update [9a0a8c1...16e9e66](https://codecov.io/gh/huggingface/transformers/pull/4050?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
