fix some comments

etc/emq.conf

@@ -189,8 +189,7 @@ mqtt.module.retainer.max_payload_size = 64KB
 mqtt.module.retainer.expired_after = 0
 
 ## Enable presence module
-## Client presence management module. Publish presence messages when
-## client connected or disconnected.
+## Publish presence messages when client connected or disconnected.
 mqtt.module.presence = on
 
 mqtt.module.presence.qos = 0