manpage: remove a reference to a removed option

DOCS/man/options.rst

@@ -2546,8 +2546,7 @@ Window
     always re-enabled when the player is paused.
 
     This is not supported on all video outputs or platforms. Sometimes it is
-    implemented, but does not work (known to happen with GNOME). You might be
-    able to work around this using ``--heartbeat-cmd`` instead.
+    implemented, but does not work (especially with Linux "desktops").
 
 ``--wid=<ID>``
     This tells mpv to attach to an existing window. If a VO is selected that