remove dependency on pkg_resources

remove dependency on pkg_resources

The dependency on ``pkg_resources`` which is part of ``setuptools`` has
been removed, so there is no longer any runtime dependency on
``setuptools``. The functionality has been replaced with
``importlib.metadata`` and ``importlib.resources`` which are both part of
Python std.lib, or via pypy dependency ``importlib-metadata`` for Python
version < 3.8 and ``importlib-resources`` for Python version < 3.7.

Change-Id: I7802fe72ff644f52ae2edde53bc8e16f016b7c45
Fixes: #885