Remove dependency on setuptools for pythran -E

[serge-sans-paille]

This should simplify the life of scipy maintainers, see #2228.

[serge-sans-paille]

@agriyakhetarpal / @rgommers is the last commit of this patchset enough for scipy? Do you need a minor release with it?

[agriyakhetarpal]

Hi @serge-sans-paille, I may not have the full context, but FWIW, since it reduces reliance on setuptools's functionality at least for building Pythran extension modules, it is a beneficial change that would be nice to incorporate in a new minor release – especially because source builds from SciPy releases were broken for an interim time period between setuptools version 73.0.0 and version 73.0.1.

[rgommers]

Thanks @serge-sans-paille! This looks like it does the job indeed.