Drop manually specified default PYTHONPATH's

[Micket]

All the trivial cases cleaned up here. Some others i could potentially partly clean up, which uses a mix of several PYTHONPATH (standard + nonstandard location, Spark is an example of such an easyconfig).

Should of course not be merged until the corresponding framework PR is merged.

• depends on prepend to $PYTHONPATH or $EBPYTHONPREFIXES in generated module files by automatically scanning for python site package directories easybuild-framework#4539

[Flamefire]

That reminds me of an old PR of mine: #13385

However all but 1 of the ECs are now deprecated and that one is fixed here. However there was also an enhancement to CI which I extracted to #20963

And a regexp I used which you might try in your tree: grep -E ": 'lib/python[^/]+/site-packages'" $(grep --files-with-matches -Er "\\beasyblock = '(ConfigureMakePythonPackage|PythonBundle)'")