Remove unused public window-property functions

Simplify the set of window-property functions to remove the
unused functions:

 meta_window_reload_properties_from_xwindow()
 meta_window_reload_properties()

And to make:

 meta_window_reload_property()

static. The code is considerably simplified by removing the
plural variants.

https://bugzilla.gnome.org/show_bug.cgi?id=587255