Use scikit-build CMake files for pycvc5 (#6543)

Use scikit-build CMake files for pycvc5 (#6543)

This PR removes copied CMake files for the pycvc5 Cython target, and instead adds a dependency on scikit-build (where those CMake files originated anyway). This keeps us up to date with fixes. Furthermore, the PR switches from distutils to the more modern setuptools. This does add another dependency but it's a fairly reasonable one. setuptools is not part of the base Python distribution, but my understanding is that it is now the de facto standard, and most package managers install it automatically with Python. The main motivation for switching is in preparation for building wheels.

This PR is a piece of this old one (#5657) which I am closing and splitting up.