Remove wrong check from conductor periodic task

It's not needed and "node_iter" is a generator.

Change-Id: I875cc421cf9e5b1b9dc146459c3a5a1fdb96d666

ironic/conductor/manager.py

@@ -1209,8 +1209,6 @@ class ConductorManager(base_manager.BaseConductorManager):
             filters={'provision_state': states.DEPLOYING,
                      'maintenance': False,
                      'reserved_by_any_of': offline_conductors})
-        if not node_iter:
-            return
 
         for node_uuid, driver, node_id, conductor_hostname in node_iter:
             # NOTE(lucasagomes): Although very rare, this may lead to a