Remove the ability to grab resize unmaximize

This is an extremely niche feature, and conflicts with the rest of our
interface being consistent about not allowing resizing while tiled or
maximized.

src/core/display.c

@@ -1922,7 +1922,6 @@ meta_display_begin_grab_op (MetaDisplay *display,
   display->grab_last_moveresize_time.tv_usec = 0;
   display->grab_last_user_action_was_snap = FALSE;
   display->grab_frame_action = frame_action;
-  display->grab_resize_unmaximize = 0;
 
   meta_display_update_cursor (display);