Refactor: doc: Change templates for generated python docs.

The custom class and module templates were present because the
autogenerated summaries for those things were not at all detailed -
basically, no members of classes and modules would be output. This in
turn led to warnings when sphinx would try to generate docs for
inherited members, especially in the IntEnum class.

Instead, get rid of those templates and instead add a new, much simpler
template that accomplishes the same thing but without causing those
warnings.

Fixes T726