[Wav2Vec2FeatureExtractor] Align documentation with code
In the code, `do_normalize` defaults to True: https://github.com/huggingface/transformers/blob/master/src/transformers/models/wav2vec2/feature_extraction_wav2vec2.py#L74

The documentation describe `do_normalize` as a desirable option to set to true, so this PR fixes the documentation to match the code.

## Before submitting
- [X] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] 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/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


_The documentation is not available anymore as the PR was closed or merged._<|||||>https://moon-ci-docs.huggingface.co/docs/transformers/pr_15468/en/model_doc/wav2vec2#transformers.Wav2Vec2FeatureExtractor.do_normalize 🎉 <|||||>Sorry for being so incredible late here<|||||>Happy to help make things better 🤗 🚀 