Fixes#9799.
Stubtest started failing on our `setuptools` stubs because of a default value added to our stdlib `distutils` stubs. The reason for this is because our `setuptools` stubs erroneously claim here that the `setuptools._distutils.core.Distribution` class is the same as the stdlib `distutils.dist.Distribution` class:
https://github.com/python/typeshed/blob/06755e10ba0d39e7e4c18fcc2663d9da564a71ad/stubs/setuptools/setuptools/_distutils/core.pyi#L3
In actual fact, they're not, and they have different default values for this parameter. But reverting the addition of the default value is the simplest short-term fix for now.
(An alternative fix would be to just merge #9795.)
* Replace all uses of StrPath, BytesPath, and AnyPath in Python 2 stubs.
* Add StrOrBytesPath as preferred alias for AnyPath.
* Replace all remaining AnyPath instances with StrOrBytesPath.
* Mark AnyPath as obsolete.
Part of #5470
Alex Waygood