Remove unused signal enum values

GtkWidget lost even more signals, so we don't need
these enum values anymore.

gtk/gtkwidget.c

@@ -511,17 +511,13 @@ enum {
   STATE_FLAGS_CHANGED,
   DIRECTION_CHANGED,
   GRAB_NOTIFY,
-  CHILD_NOTIFY,
   MNEMONIC_ACTIVATE,
   MOVE_FOCUS,
   KEYNAV_FAILED,
   POPUP_MENU,
   ACCEL_CLOSURES_CHANGED,
-  DISPLAY_CHANGED,
   CAN_ACTIVATE_ACCEL,
   QUERY_TOOLTIP,
-  DRAG_FAILED,
-  STYLE_UPDATED,
   LAST_SIGNAL
 };