Revert "Document new feature RTSP trickplay support."

This reverts commit 814eafd9.

New features that are not self-contained and modify src/ are not
welcomed in -bugfix branches without pre-existent consensus.

NEWS

 Changes between 0.9.6 and 0.9.7-git:
 ------------------------------------
-Features:
- * RTSP trickplay support
+
 
 Changes between 0.9.5 and 0.9.6:
 --------------------------------