setup.py: drop deprecated setup_requires, fixes #6068

We now use pyproject.toml for that.

Also, drop the >=1.7 requirement for setuptools_scm,
that was from 2015 and we assume it is not used any
more anyway.

setup.py

@@ -306,7 +306,6 @@ setup(
     },
     cmdclass=cmdclass,
     ext_modules=ext_modules,
-    setup_requires=['setuptools_scm>=1.7'],
     install_requires=install_requires,
     extras_require=extras_require,
     python_requires='>=3.9',