tooltip: Remove an unused gdk_surface_get_root_coords call

The tx and ty variables are not used, so don't
bother setting them.

gtk/gtktooltip.c

@@ -689,8 +689,6 @@ gtk_tooltip_show_tooltip (GdkDisplay *display)
   tooltip = g_object_get_qdata (G_OBJECT (display), quark_current_tooltip);
 
   {
-    gint tx, ty;
-
     surface = tooltip->last_surface;
 
     if (!GDK_IS_SURFACE (surface))
@@ -702,7 +700,6 @@ gtk_tooltip_show_tooltip (GdkDisplay *display)
     x = round (px);
     y = round (py);
 
-    gdk_surface_get_root_coords (surface, x, y, &tx, &ty);
     tooltip_widget = _gtk_widget_find_at_coords (surface, x, y, &x, &y);
   }