Remove warning when Annotion enum is created

[amyeroberts]

What does this PR do?

The Annotion enum was deprecated in #26941.

I asked for there to be a deprecation warning to let users know if they chose to use the enum. This was overly defensive and in light of recent complaints of objects being removed/moved from the library (even if they were never meant to be used directly).

However, complete oversight on my part is that the init of the enum will be created any time any object from the image_utils module file is imported - resulting in verbose error messages unrelated to what the user was trying to do - my bad.

This PR removed the warning from the enum itself and adds it into a validation check that happens on annotations.

It ultimately means that we might break things when we remove Annotion - but this is likely to be very unlikely and with a simple, quick resolution.

Partially resolves #28042

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 docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[patrickvonplaten]

Nice!