Replace input_values_processing with unpack_inputs

[amyeroberts]

What does this PR do?

Updates Hubert and Wav2Vec2 to use the repo standard unpack_inputs decorator instead of input_values_processing. Previously, TensorFlow models use input_values_processing, a function which processed inputs ready to be passed to the TF layers. This was removed and replaced with unpack inputs, see #16051. For some reason, wav2vec2 wasn't part of this update. A bug was reported, but the conversation and details can't be found in the discord 😢

This PR also updates any relevant tests:

• Adds unittest.skip decorator so tests are marked as skipped rather than passed
• Modifies batch sizes for tests that were previously skipped for OOM to make sure logic is fully tested.
• Adds back tests which shouldn't have been skipped. This caught the issue with loss not being calculated (see below)

Note: The loss calculation for TFHubertForCTC wasn't being calculated properly. Without the unpack_inputs decorator, when model.fit was being called, labels were passed into the model as part of the input_values dictionary. These were then processed and part of the inputs dictionary. However, labels was always taken from the function kwargs and so loss calculation skipped. This is why the previous test 'returned the wrong shape'. The issue was resolved for TFWav2Vec2ForCTC in a previous PR #18014

Before submitting

• 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,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? 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, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Thanks for the cleanup!

[Rocketknight1]

This looks so much cleaner now