Fix audio feature extractor deps
# What does this PR do?

The PR #21998 refactored many of the audio feature extractors to use a numpy backed for log Mel feature extraction (as opposed to `torchaudio` as was done previously). However, some of the feature extractors still required the `"speech"` backend for import, which states `torchaudio` as its sole dependency:
https://github.com/huggingface/transformers/blob/6eedfa6dd15dc1e22a55ae036f681914e5a0d9a1/src/transformers/utils/import_utils.py#L648-L650

This PR updates these four feature extractors to no longer require `"speech"`, since they're now numpy only.
_The documentation is not available anymore as the PR was closed or merged._