Remove the redundant default value

When get a value from a dict, it returns the value of the key,
if the key does not existed in the dict, the dafault value is
None, So we don't need to specify the default None value again.

Change-Id: Iff4a9c14e356f8ec59fc79ef00aa8207bf926c9e

mistral/api/controllers/v2/event_trigger.py

@@ -90,7 +90,7 @@ class EventTriggersController(rest.RestController):
         values = event_trigger.to_dict()
 
         for field in UPDATE_NOT_ALLOWED:
-            if values.get(field, None):
+            if values.get(field):
                 raise exc.EventTriggerException(
                     "Can not update fields %s of event trigger." %
                     UPDATE_NOT_ALLOWED

mistral/rpc/kombu/kombu_listener.py

@@ -81,7 +81,7 @@ class KombuRPCListener(ConsumerMixin):
 
             correlation_id = message.properties['correlation_id']
 
-            queue = self._results.get(correlation_id, None)
+            queue = self._results.get(correlation_id)
 
             if queue:
                 result = {

mistral/rpc/kombu/kombu_server.py

@@ -227,7 +227,7 @@ class KombuRPCServer(rpc_base.RPCServer, kombu_base.Base):
 
         is_async = request.get('async', False)
         rpc_ctx = request.get('rpc_ctx')
-        redelivered = message.delivery_info.get('redelivered', None)
+        redelivered = message.delivery_info.get('redelivered')
         rpc_method_name = request.get('rpc_method')
         arguments = self._deserialize_message(request.get('arguments'))
         correlation_id = message.properties['correlation_id']