Remove unnecessary model_type arg in example
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4771?src=pr&el=h1) Report
> Merging [#4771](https://codecov.io/gh/huggingface/transformers/pull/4771?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/e645b9ab9407e1c1b2c168317dc79fe13fc6e0b4&el=desc) will **decrease** coverage by `0.81%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4771/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4771?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #4771      +/-   ##
==========================================
- Coverage   77.31%   76.49%   -0.82%     
==========================================
  Files         128      128              
  Lines       21059    21059              
==========================================
- Hits        16281    16110     -171     
- Misses       4778     4949     +171     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4771?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_gpt2.py](https://codecov.io/gh/huggingface/transformers/pull/4771/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19ncHQyLnB5) | `31.32% <0.00%> (-55.07%)` | :arrow_down: |
| [src/transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4771/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ191dGlscy5weQ==) | `89.91% <0.00%> (-0.25%)` | :arrow_down: |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4771/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `74.27% <0.00%> (+0.41%)` | :arrow_up: |
| [src/transformers/modeling\_openai.py](https://codecov.io/gh/huggingface/transformers/pull/4771/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19vcGVuYWkucHk=) | `82.03% <0.00%> (+1.35%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/4771?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/4771?src=pr&el=footer). Last update [e645b9a...7ad3a66](https://codecov.io/gh/huggingface/transformers/pull/4771?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
