CHANGES: Remove already applied CHANGES update

Change-Id: Iee7163bc732d58c5cbaa2cfab1f5aab4a412060a

doc/CHANGES-staging/hide_messaging_ami_events

-Subject: Messaging
-
-In order to reduce the amount of AMI and ARI events generated,
-the global "Message/ast_msg_queue" channel can be set to suppress
-it's normal channel housekeeping events such as "Newexten",
-"VarSet", etc. This can greatly reduce load on the manager
-and ARI applications when the Digium Phone Module for Asterisk
-is in use.  To enable, set "hide_messaging_ami_events" in
-asterisk.conf to "yes"  In Asterisk versions <18, the default
-is "no" preserving existing behavior.  Beginning with
-Asterisk 18, the option will default to "yes".