PEP 517 backend: get_requires_for_build_wheel shouldn't include setuptools

[pfmoore]

See pypa/pip#5743 (comment).

As the backend is part of setuptools, it doesn't need to request that setuptools is installed in get_requires_for_build_wheel. (And it certainly shouldn't be allowing any version - at a minimum it needs a version that supports the PEP 517 backend, but that's not important as it shouldn't be there in the first place 😉 )

[pfmoore]

#1594 created for the fix. I also corrected the same mistake in get_requires_for_build_sdist.

[jaraco]

Thanks for the patch, @pfmoore . This is releasing as 40.6.3.