Consolidate `assert_XXX_enabled` type calls to managers

There are multiple implementations of the various assert_XXX_enabled
methods. These have been consolidated to rely on the appropriate
manager objects (e.g. domain uses assignment_api, user now uses
identity_api).

``keystone.token.core.validate_auth_info`` has been deprecated
with no plans to be superseded as the new ``assert_XXXX_enabled``
methods now cover the functionality.

This is another step in the process to deprecate the functionality
from the token_api (and move relevant logic either the
token provider or other relevant locations).

Change-Id: I450daaca946e9695ff30e058adecef6ef0b9058a
bp: non-persistent-tokens
Merge "Consolidate `assert_XXX_enabled` type calls to managers"