Remove old style setup.py?

[truth-quark]

This comes from PyCharm warning that the f90nml & mule dependencies are not satisfied in project requirements.

The requirements are in pyproject.toml but not setup.py. Removing setup.py fixed the warnings, indicating PyCharm confusion with having both build related files in the root dir.

Tasks:

• Check Complete Guide to pyproject.toml: replace setup.py and requirements.txt
• Check Modernise setup.py
• Determine if setup.py is needed
  • Configure versioneer via pyproject.toml?