Remove an entry from CHANGES that is already in UPGRADE.txt (where it should be).

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@233967 65c4cc65-6c06-0410-ace0-fbb531ad65f3

CHANGES

@@ -365,9 +365,6 @@ Miscellaneous
 
 SIP Changes
 -----------
- * The prematuremedia option is disabled by default.  Applications requiring
-   SIP early audio must use the Progress() dialplan application to generate
-   the 183 progress message.
  * Added support for SUBSCRIBE/NOTIFY with dialog-info based call pickups.
    Snom phones use this for call pickup of extensions that the phone is
    subscribed to.