Removed `Bert` interdependency in `tokenization_electra.py`
# What does this PR do?


Related to #19303 
Removes `bert` dependency from `tokenization_electra.py`


## 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.
- [ ] 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).
- [ ] Did you write any new necessary tests?


## Who can review?
 @sgugger 
_The documentation is not available anymore as the PR was closed or merged._<|||||>> Thanks a lot for working on this one! It's missing a few copied froms, I left suggestions. Once you're done, be sure to run `make style` on your branch (for code-formatting) and we should be good to merge!

`make style` changes a lot of files.<|||||>Make sure you install the specific versions of black that we use with `pip install -e .[quality]`, it's probably because you don't ahve the same version as the one we use.