Remove dependency of Roberta in Blenderbot
Author: rchan26
Pull request: yes

Hi @sgugger,

This PR looks to address https://github.com/huggingface/transformers/issues/19303: the RobertaTokenizer dependency has been removed from `BlenderbotTokenizer` and the RobertaFastTokenizer dependency has been removed from `BlenderbotTokenizerFast`.

I did encounter an error when running `pytest tests/models/blenderbot/test_tokenization_blenderbot.py`, and I got the following error:
```
========================================================================= test session starts =========================================================================
platform darwin -- Python 3.10.4, pytest-7.1.3, pluggy-1.0.0
rootdir: /Users/rchan/Library/CloudStorage/OneDrive-TheAlanTuringInstitute/huggingface/transformers, configfile: setup.cfg
collected 4 items

tests/models/blenderbot/test_tokenization_blenderbot.py F...                                                                                                    [100%]

============================================================================== FAILURES ===============================================================================
___________________________________________________ Blenderbot3BTokenizerTests.test_3B_tokenization_same_as_parlai ____________________________________________________

self = <tests.models.blenderbot.test_tokenization_blenderbot.Blenderbot3BTokenizerTests testMethod=test_3B_tokenization_same_as_parlai>

    def test_3B_tokenization_same_as_parlai(self):
        assert self.tokenizer_3b.add_prefix_space
>       assert self.tokenizer_3b([" Sam", "Sam"]).input_ids == [[5502, 2], [5502, 2]]
E       assert [[1, 5502, 2], [1, 5502, 2]] == [[5502, 2], [5502, 2]]
E         At index 0 diff: [1, 5502, 2] != [5502, 2]
E         Use -v to get more diff

tests/models/blenderbot/test_tokenization_blenderbot.py:48: AssertionError
------------------------------------------------------------------------ Captured stderr call -------------------------------------------------------------------------
Special tokens have been added in the vocabulary, make sure the associated word embeddings are fine-tuned or trained.
========================================================================== warnings summary ===========================================================================
src/transformers/testing_utils.py:28
  /Users/rchan/Library/CloudStorage/OneDrive-TheAlanTuringInstitute/huggingface/transformers/src/transformers/testing_utils.py:28: DeprecationWarning: The distutils package is deprecated and slated for removal in Python 3.12. Use setuptools or check PEP 632 for potential alternatives
    from distutils.util import strtobool

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================================================================= short test summary info =======================================================================
FAILED tests/models/blenderbot/test_tokenization_blenderbot.py::Blenderbot3BTokenizerTests::test_3B_tokenization_same_as_parlai - assert [[1, 5502, 2], [1, 5502, 2]...
=============================================================== 1 failed, 3 passed, 1 warning in 2.15s ================================================================
```

Any idea on what I have done wrong here?

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [x] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [x] Did you write any new necessary tests?

Comments:
_The documentation is not available anymore as the PR was closed or merged._

Hi @sgugger, I have now removed the global ` # Copied from` statements, and replaced them with Copied from statements to the individual methods that I am copying into the Blenderbot classes. This has resolved my earlier problem and now `pytest tests/models/blenderbot/test_tokenization_blenderbot.py` runs without error.

Currently, my PR now fails `python utils/check_copies.py` as there are two methods named `mask_token` in the `RobertaTokenizerFast`. This means that I currently have two `# Copied from transformers.models.roberta.tokenization_roberta_fast.RobertaTokenizerFast.mask_token` statements and so there's a matching problem.

How should I deal with the case where there are two methods with the same name?

I've just seen that someone had a similar issue with copying over a method with a setter: https://github.com/huggingface/transformers/pull/19408#pullrequestreview-1134731877.

I have now followed the advice on this PR and have removed my Copied from statement on the setter for `mask_token`. Seems like all tests pass now 🙂