BLD: remove `pkg_resources` usage from `setup.py`

[fangchenli]

pkg_resources is deprecated and needs to be removed.

After #49115, version checks in setup.py are unnecessary. And MACOSX_DEPLOYMENT_TARGET should be set in meson script instead of setup.py.

Maybe bump MACOSX_DEPLOYMENT_TARGET as well?

[jorisvandenbossche]

I suppose we can close this issue since setup.py is no longer used? (I don't think there is a need to fix the pkg_resources usage there)

Not really sure about your mention of MACOSX_DEPLOYMENT_TARGET though (that is still only used in setup.py and not in the meson configuration)

(PR removing setup.py instructions -> #62389)