Remove wheel from build-system.requires

[bmerry]

See https://setuptools.pypa.io/en/latest/userguide/quickstart.html, which says

Historically this documentation has unnecessarily listed wheel in the
requires list, and many projects still do that. This is not recommended.
The backend automatically adds wheel dependency when it is required, and
listing it explicitly causes it to be unnecessarily required for source
distribution builds. You should only include wheel in requires if you
need to explicitly access it during build time (e.g. if your project
needs a setup.py script that imports wheel).