Fix unused argument triggering flake8

Strangely this doesn't occur on master but did here:
https://review.opendev.org/#/c/727089/3

Change-Id: Ie2ff53d8ed2db03f70bd2ab7789028b5b7a5e91d

zuul/ansible/base/callback/zuul_stream.py

@@ -663,7 +663,7 @@ class CallbackModule(default.CallbackModule):
                     host=hostname, status=status, msg=msg))
         else:
             self._log("{host} | {status}".format(
-                host=hostname, status=status, msg=msg))
+                host=hostname, status=status))
         if result_dict:
             result_string = json.dumps(result_dict, indent=2, sort_keys=True)
             for line in result_string.split('\n'):