Generate: deprecation timeline for parameterization though the model config
# What does this PR do?

We had a warning about deprecating the parameterization of `.generate()` through the model config, but there was no specific date. This PR makes it clear it will go away in `v4.32`.

The extra parameters and code to allow the old and the new way of parameterizing `.generate()` to live together are causing a myriad of issues, so let's get rid of them :)
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_24457). All of your documentation changes will be reflected on that endpoint.<|||||>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.

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