refactor(enum): rename python_type -> enum, enum_labels -> labels on EnumInfo

refactor(enum): rename python_type -> enum, enum_labels -> labels on EnumInfo

The previous name were lifted from the composite adapters. However, that
class would have had a more ambiguous "type" attribute, and "types" for
the fields, hence the decision of using "python_" and "fields_" prefix
to disambiguate.

In the enum adapters context, enum is not ambiguous, so a more natural
name seems preferred.