windowcontrols: No need to listen to scale factor changes

This is a GTK3 leftover where the icons were manually drawn and sized.
Now that they're managed by actual widgets that enforce a correct size
that is independent of scale factor, this is no longer necessary.

Fixes warnings about resizes during allocate caused by scale change
notification during allocation of GtkWindow.

gtk/gtkwindowcontrols.c

@@ -382,7 +382,6 @@ window_notify_cb (GtkWindowControls *self,
       pspec->name == I_("maximized") ||
       pspec->name == I_("modal") ||
       pspec->name == I_("resizable") ||
-      pspec->name == I_("scale-factor") ||
       pspec->name == I_("transient-for"))
     update_window_buttons (self);
 }