Django provides a utility function named func_accepts_kwargs(), which

checks a function's signature to determine if it accepts a **kwargs

argument.
We perform this check from time to time, when trying to work around

legacy extension interfaces. There are currently two cases where we were

performing this check ourselves using getargspec, which is deprecated

and warns on Python 3.
This change switches to Django's method, saving us the deprecation

warning and slimming down the code.
There's also an old unused getargspec import that has been removed.

Unit tests pass.