Remove Python shim once loading rev actions as module is deprecated in Python agent

Currently in Python, revocation actions are imported as Python modules and run with a separate `execute()` function: [ref](https://github.com/keylime/keylime/blob/37d338fe3056fdb9345f936902426ac22d9afaf4/keylime/keylime_agent.py#L583-L590)

We match this functionality with some of the changes in #321.

However, this functionality will be deprecated in Python and at that point we do not need to match it.

Start by reviewing the Python reference in keylime_agent.py around lines 583-590 and the related changes in issue #321. Confirm how revocation actions are currently matched in rust-keylime and whether the Python module-loading behavior is deprecated; done means the obsolete shim is removed without preserving that compatibility behavior.

Written by the indexing model from the issue text.