Remove deprecated pkg_resources usage

[georgkrause]

There is a pretty elegant solution in rspeer#6 which should be ported before the next release

[georgkrause]

This cannot be done as long as we want to support python 3.8, I am therefore removing it from the Milestone

[pdhall99]

This cannot be done as long as we want to support python 3.8, I am therefore removing it from the Milestone

importlib-resources could be added as an conditional dependency for python < 3.9, and then

import sys

if sys.version_info < (3, 9):
    from importlib_resources import files
else:
    from importlib.resources import files

I can make the changes if you'd accept this as a solution?

[georgkrause]

Python 3.8 is only supported until October 31, so instead of adding complexity I'd prefer to only remove the deprecated function when we stop supporting python 3.8.