Remove `importlib_resources` dependency once Python3.8 support is dropped

[sbadithe]

The reason we have the importlib_resources dependency is because the importlib.resources.files API is only supported for 3.9+ and so we need a backport. Once we drop support for 3.8, we can remove this dependency, as we will be able to use importlib directly.

This issue was created as part of this PR: #1584, which in turn resolved #1582.