Remove use of pkg_resources when not supporting Python 3.7 any more

[felixdivo]

Currently, a fallback to pkg_resources.iter_entry_points is used in can/interfaces/__init__.py. However, the setuptools docs state:

Use of pkg_resources is discouraged in favor of importlib.resources, importlib.metadata, and their backports (resources, metadata). Please consider using those libraries instead of pkg_resources.

On Python 3.8+, importlib.metadata is part of the standard library, so there should be no need to keep pkg_resources.iter_entry_points around, right?

The PR #1110 is related.