The update tracking code was ugly and using deprecated drawing APIs. It
was also in the wrong place.
So instead of trying to keep it working, I'll remove it. We need to find
a better way to put it and make it work there.
... and gdk_screen_get_window_stack().
Those functions were originally added in
5afb4f0f11 but do not seem to be used as
they are not implemented anywhere but in X.
As GDK is not meant to fulfill window management functionality I'm going
to remove these functions without replacements.
... and gdk_screen_get_width_mm() and gdk_screen_get_height_mm() and
the shortcut counterparts that call these functions on the default
screen.
Modern display servers don't provide an ability to query the size of a
screen or display so we shouldn't allow that either.
