Remove frame handler prototype

I messed up the merge.

clients/window.h

@@ -210,10 +210,6 @@ void
 window_set_keyboard_focus_handler(struct window *window,
 				  window_keyboard_focus_handler_t handler);
 
-void
-window_set_frame_handler(struct window *window,
-			 window_frame_handler_t handler);
-
 void
 window_set_title(struct window *window, const char *title);