removing XLMConfig inheritance from FlaubertConfig
# What does this PR do?
related to  #19303
Removes `XLMConfig` dependency from `FlaubertConfig`

the `__init__` from `FlaubertConfig` differs from `XLMConfig` in the following ways:

- `pre_norm` and `layerdrop` are specific to `FlaubertConfig`. So, I have not added and `#Copied from ...`


## 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._<|||||>Can you just put the PR as ready for review and remove WIP from the title? I can't merge draft PRs :-)<|||||>> Can you just put the PR as ready for review and remove WIP from the title? I can't merge draft PRs :-)

Done. Thanks:)<|||||>Thanks for your contribution!