Remove atheris

[srittau]

Atheris doesn't support Python 3.12 and can't be installed on Ubuntu 24.04 (which is used in GitHub Actions), which is why we needed to disable stubtest. The last upstream commit was 11 months ago. According to google/atheris#82, the package is still semi-maintained, but currently I don't see that. I propose to remove it from typeshed for now. If atheris is ever updated upstream, we can always restore the package.

[Avasam]

If it's being a blocker for us I'm fine with it. Especially since restoring the stubs if atheris is updated is as simple as reverting 2 commits.

Might wanna add a mention in google/atheris#83 for the community of users that are using typed atheris. (which I kinda did just by linking the issue since it'll appear there and links back here for the reasoning)

[srittau]

I left a note.

[juntyr]

atheris has a new version v3.0 that supports Python 3.11, 3.12, 3.13

[srittau]

Thanks, #15140