Remove duplicate code in Objects create() function

Remove duplicate code updates.pop('id', None) in create() function.
Because if self.obj_attr_is_set('id'):
            raise exception.ObjectActionError(action='create',
            reason='already created')
already make sure object doesn't have 'id' values, which means that
'id' won't appear in updates.

Change-Id: I582ef8857b32c07ea8ba1eb5fc1e64516110f3ce

nova/objects/aggregate.py

@@ -71,7 +71,6 @@ class Aggregate(base.NovaPersistentObject, base.NovaObject):
                                                     "create.start",
                                                     payload)
         metadata = updates.pop('metadata', None)
-        updates.pop('id', None)
         db_aggregate = db.aggregate_create(context, updates, metadata=metadata)
         self._from_db_object(context, self, db_aggregate)
         payload['aggregate_id'] = self.id