Pipelines: use tokenizer.max_len
fix #4224 by passing tokenizer.max_len to `tokenizer.batch_encode_plus`

# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4236?src=pr&el=h1) Report
> Merging [#4236](https://codecov.io/gh/huggingface/transformers/pull/4236?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/cf08830c2868c5335b1657f95779f370862e3a28&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4236/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4236?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #4236      +/-   ##
==========================================
- Coverage   78.38%   78.37%   -0.02%     
==========================================
  Files         120      120              
  Lines       19918    19918              
==========================================
- Hits        15613    15611       -2     
- Misses       4305     4307       +2     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4236?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/pipelines.py](https://codecov.io/gh/huggingface/transformers/pull/4236/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9waXBlbGluZXMucHk=) | `76.56% <ø> (+0.19%)` | :arrow_up: |
| [src/transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4236/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ191dGlscy5weQ==) | `90.48% <0.00%> (-0.49%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4236/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `92.93% <0.00%> (+0.16%)` | :arrow_up: |

------

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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4236?src=pr&el=footer). Last update [cf08830...158cd06](https://codecov.io/gh/huggingface/transformers/pull/4236?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>This PR is actually very related to this issue: #4501<|||||>Abandoning.