stop relying on `imp` (will no longer be available in Python 3.12)

[boegel]

imp is deprecated since Python 3.4, replaced with importlib, will be removed in Python 3.12 stdlib, cfr. https://docs.python.org/3.11/library/imp.html

Currently used in:

• easybuild/tools/filetools.py
• easybuild/tools/hooks.py