Remove xxhash types (not before April 2023)

[faresbakhit]

ifduyue/python-xxhash added type hints to master the last month (here in #4689), however the latest release doesn't ship with __init__.pyi nor py.typed. so wait until xxhash's next release and remove ./stubs/xxhash from here?

[JelleZijlstra]

Thanks! Our rule is to remove the stubs 6 months after the first release that ships stubs.

[srittau]

xxhash doesn't seem to ship with py.typed, and I can't find any mention of py.typed in the repository either. I am going to close this until xxhash adds support for type hints.

[hauntsaninja]

Sort of seems the intention was to add a py.typed though (ifduyue/python-xxhash#51 talks about PEP 561), so could mention it to the upstream project if anyone is so inclined.

[AlexWaygood]

Upstream just cut a release with a py.typed file: #8935