[docs] Remove the get_originu() method
[docs] Remove the get_originu() method

The gtk_clutter_viewport_get_originu() method was removed from
the public API, hence we should remove it from the API reference
as well.

Distrotech/clutter-gtk,GNOME/clutter-gtk,Distrotech/clutter-gtk,GNOME/clutter-gtk,Distrotech/clutter-gtk