Update setup_requirements to match pyproject.toml

[kubinski]

Updated setup_requirements to match the requirements listed in pyproject.toml.

[lmctv]

@pyca/pynacl-core @dstufft I seem to remember using setup_requirements is deprecated when building with pip. If this is the case, I think we should add a comment before the empty list in setup.py

[reaperhulk]

setup_requires are deprecated by pyproject.toml but we need to retain them until we decide to drop support for pips without pyproject.toml support (aka everything except the latest release right now)

[lmctv]

It seems this is still useful. Will merge.

[kitterma]

The problem with this change is what wheel is only required if you are building a wheel. Not everyone does this, so it seems odd to require it. Particularly since wheel being available to pip is the default in a virtualenv. Since I'm not building a wheel, now I have to carry this pointless requirement or patch the project.

[reaperhulk]

@kitterma Yeah I'd be happy to take a PR removing that. We don't do it in pyca/cryptography and there's no reason to do it here.

[kitterma]

@reaperhulk OK. See #596. Thanks.