Remove redundant priority override code from service steps

Currently, service steps are only supported as a user-requested action.
This change removes references to overriding priorities for service
steps as these overrides will have no effect and may cause confusion.

Change-Id: I35a8b59b17fdff3161df835903acec529e732c4f

ironic/drivers/modules/agent_base.py

@@ -854,14 +854,7 @@ class AgentBaseMixin(object):
         :returns: A list of service step dictionaries, if an error
                   occurs, then an empty list is returned.
         """
-        new_priorities = {
-            'erase_devices': CONF.deploy.erase_devices_priority,
-            'erase_devices_metadata':
-                CONF.deploy.erase_devices_metadata_priority,
-        }
-        return get_steps(
-            task, 'service',
-            override_priorities=new_priorities)
+        return get_steps(task, 'service')
 
     @METRICS.timer('AgentBaseMixin.refresh_steps')
     def refresh_steps(self, task, step_type):

ironic/tests/unit/drivers/modules/test_agent.py

@@ -1114,9 +1114,7 @@ class TestAgentDeploy(CommonTestsMixin, db_base.DbTestCase):
         with task_manager.acquire(self.context, self.node.uuid) as task:
             steps = self.driver.get_service_steps(task)
             mock_get_steps.assert_called_once_with(
-                task, 'service',
-                override_priorities={'erase_devices': None,
-                                     'erase_devices_metadata': None})
+                task, 'service')
         self.assertEqual(mock_steps, steps)
 
     @mock.patch.object(agent_base, 'get_steps', autospec=True)