Drop legacy distutils in setup.py

[hugovk]

Distutils is not recommended for use and unnecessary for modern Python environments. Use only setuptools instead. From docs.python.org/3/library/distutils.html:

Most Python users will not want to use this module directly, but instead use the cross-version tools maintained by the Python Packaging Authority. In particular, setuptools is an enhanced alternative to distutils ...
The recommended pip installer runs all setup.py scripts with setuptools, even if the script itself only imports distutils. Refer to the Python Packaging User Guide for more information.