Removed old window clip balloon code

This code was used to create the window where the workspace name was showed
to the user. The code now use the standar balloon system, therefore this code
is not used anymore and can be removed.

src/screen.h

@@ -229,8 +229,6 @@ typedef struct _WScreen {
     WAppIconChain *global_icons;       /* for omnipresent icons chain in clip */
     int global_icon_count;	       /* How many global icons do we have */
 
-    Window clip_balloon;	       /* window for workspace name */
-
     int keymove_tick;
     struct RContext *rcontext;	       /* wrlib context */