Use `setuptools_scm` instead of custom versioning script

[maxnoe]

Please describe the use case that requires this feature.

It's much nicer to use, no code in repo needed and better integration with setuptools:
https://setuptools-scm.readthedocs.io/en/latest/

[maxnoe]

The pyproject.toml now contains setuptools_scm, but it is in fact not used. The custom version script is still there.