Remove pkg resources deprecations

[jakubpiatkowski]

Introduced changes according to deprecation warnings:

• DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
• DeprecationWarning: Deprecated call to pkg_resources.declare_namespace('fs').

Fixes: #2959

[anderssonjohan]

@jakubpiatkowski Since this library still supports older python versions, does the import of importlib.metadata work everywhere or is it necessary to make a try-except with importlib_metadata etc? I may be wrong but I think we did that before when supporting python 3.7.