Dropped stored role name/description and other superflous fields

For name and description, we'll derive these from the role_field and
content type, which is much better for lots of reasons (eg changing text
the future). Also ditched the rest of the fields comming from the
standard common base model, we didn't use them and they cost several
indexes on the table.

awx/main/signals.py

@@ -127,11 +127,10 @@ def create_user_role(instance, **kwargs):
         Role.objects.get(
             content_type=ContentType.objects.get_for_model(instance),
             object_id=instance.id,
-            name = 'User Admin'
+            role_field='admin_role'
         )
     except Role.DoesNotExist:
         role = Role.objects.create(
-            name = 'User Admin',
             role_field='admin_role',
             content_object = instance,
         )