[WIP] Fix `assert` statements found in modeling files
# What does this PR do?

Fixing unnecessary `assert` statements under modeling code. This was motivated by the fact that contributing to `transformers` often requires a lot of copying from existing code, and while `assert` statements are [undesirable in new PRs](https://github.com/huggingface/transformers/pull/16402#discussion_r881715669), a lot of existing code includes `assert` statements.

I was just going to fix it for `Speech2Text` as referenced above, but found many instances of it throughout the codebase.

It's actually not entirely clear to me where `assert` is not desirable. For utility functions like `convert_*_utils.py` it seems forgivable (used by advanced developers anyway), but correct me if I'm wrong (otherwise there are hundreds of instances to fix).  

## 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?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@sgugger 

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_17598). All of your documentation changes will be reflected on that endpoint.<|||||>Can you solve the merge conflicts? This should re-trigger the CI and we will see if the errors persist (there were some outage on the Hub this weekend).<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.