test: remove unused line

Author: rpenido

lti_consumer/tests/unit/test_lti_xblock.py

@@ -1989,7 +1989,6 @@ def runtime_service_side_effect(_block, service_name):
                 return mock_i18n_service
             if service_name == 'configuration':
                 return mock_config_service
-            return None
 
         self.xblock.runtime.service.side_effect = runtime_service_side_effect