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
Merge "Remove duplicate code in Objects create() function"