Update sys.monitoring.rst

Author: gaogaotiantian

Doc/library/sys.monitoring.rst

@@ -319,13 +319,6 @@ To register a callable for events call
 Functions can be unregistered by calling
 ``sys.monitoring.register_callback(tool_id, event, None)``.
 
-Callback functions can be registered and unregistered at any time.
-
-Callbacks are called only once regardless if the event is turned on both
-globally and locally. As such, if an event could be turned on for both global
-and local events by your code then the callback needs to be written to handle
-either trigger.
-
 
 Callback function arguments
 '''''''''''''''''''''''''''