Remove prototype folder

[NicolasHug]

We haven't graduated anything from prototype in 3+ years, and it's becoming annoying to remove it for every single release.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/9505

• 📄 Preview Python docs built from this PR

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❌ 2 New Failures, 1 Unrelated Failure

As of commit fa06130 with merge base 4252acb ():

NEW FAILURES - The following jobs have failed:

• Build M1 Wheels / pytorch/vision / build-wheel-py3_10-cpu (gh)
• Build M1 Wheels / pytorch/vision / upload / upload-wheel-py3_10-cpu (gh)
  Unable to download artifact(s): Artifact not found for name: pytorch_vision__3.10_cpu_

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Tests / unittests-macos (3.10, macos-m1-stable) / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[meta-codesync]

@NicolasHug has imported this pull request. If you are a Meta employee, you can view this in D107229206.

[github-actions]

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