window: Remove call to gdk_window_set_icon()
window: Remove call to gdk_window_set_icon()

Also remove all the functions taking care of it. This is now handled by
the X11 backend directly. And the other backends ignored this function
anyway.

davidgumberg/gtk,chergert/gtk,ahodesuka/gtk,davidgumberg/gtk,Adamovskiy/gtk,davidgumberg/gtk,ahodesuka/gtk,jigpu/gtk,alexlarsson/gtk,bratsche/gtk-,grubersjoe/adwaita,alexlarsson/gtk,davidt/gtk,grubersjoe/adwaita,Adamovskiy/gtk,Lyude/gtk-,davidgumberg/gtk,jadahl/gtk,msteinert/gtk,Adamovskiy/gtk,msteinert/gtk,Sidnioulz/SandboxGtk,jessevdk/gtk,jessevdk/gtk,grubersjoe/adwaita,simokivimaki/gtk,bratsche/gtk-,jadahl/gtk,simokivimaki/gtk,Adamovskiy/gtk,alexlarsson/gtk,ahodesuka/gtk,Lyude/gtk-,simokivimaki/gtk,Distrotech/gtk2,simokivimaki/gtk,ebassi/gtk,Adamovskiy/gtk,jigpu/gtk,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,davidt/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,alexlarsson/gtk,simokivimaki/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,bratsche/gtk-,ahodesuka/gtk,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,jadahl/gtk,grubersjoe/adwaita,bratsche/gtk-,msteinert/gtk,Lyude/gtk-,simokivimaki/gtk,grubersjoe/adwaita,alexlarsson/gtk,jessevdk/gtk,davidgumberg/gtk,Distrotech/gtk2,jessevdk/gtk,jadahl/gtk,Distrotech/gtk2,Lyude/gtk-,ebassi/gtk,ahodesuka/gtk,ebassi/gtk,alexlarsson/gtk,msteinert/gtk,Lyude/gtk-,jigpu/gtk,bratsche/gtk-,chergert/gtk,Adamovskiy/gtk,jigpu/gtk,ebassi/gtk,jadahl/gtk,davidt/gtk,davidgumberg/gtk,jessevdk/gtk,jigpu/gtk,grubersjoe/adwaita,Distrotech/gtk2,jadahl/gtk,ahodesuka/gtk,msteinert/gtk,jessevdk/gtk,alexlarsson/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,alexlarsson/gtk,ebassi/gtk,jigpu/gtk,ahodesuka/gtk,davidt/gtk,jadahl/gtk,bratsche/gtk-,chergert/gtk,davidt/gtk,davidgumberg/gtk,jadahl/gtk,chergert/gtk,Distrotech/gtk2,grubersjoe/adwaita,Lyude/gtk-,davidt/gtk,Lyude/gtk-,Adamovskiy/gtk,Sidnioulz/SandboxGtk,chergert/gtk,msteinert/gtk,chergert/gtk,Distrotech/gtk2,ebassi/gtk,chergert/gtk,jessevdk/gtk