treeview: remove needless duplicate gtk_widget_set_parent_window() call
treeview: remove needless duplicate gtk_widget_set_parent_window() call

This same call happens a few lines above.

davidgumberg/gtk,Adamovskiy/gtk,grubersjoe/adwaita,chergert/gtk,jigpu/gtk,ahodesuka/gtk,jessevdk/gtk,jessevdk/gtk,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jessevdk/gtk,davidgumberg/gtk,ahodesuka/gtk,davidgumberg/gtk,jigpu/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,ahodesuka/gtk,jessevdk/gtk,jadahl/gtk,jadahl/gtk,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jessevdk/gtk,jigpu/gtk,alexlarsson/gtk,davidgumberg/gtk,jadahl/gtk,grubersjoe/adwaita,ahodesuka/gtk,grubersjoe/adwaita,grubersjoe/adwaita,chergert/gtk,Lyude/gtk-,Lyude/gtk-,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,ahodesuka/gtk,jigpu/gtk,Lyude/gtk-,jessevdk/gtk,Adamovskiy/gtk,ahodesuka/gtk,Adamovskiy/gtk,jigpu/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,Lyude/gtk-,Adamovskiy/gtk,Lyude/gtk-,jigpu/gtk,ahodesuka/gtk,grubersjoe/adwaita,chergert/gtk,Adamovskiy/gtk,davidgumberg/gtk,alexlarsson/gtk,Adamovskiy/gtk,alexlarsson/gtk,davidgumberg/gtk,jadahl/gtk,jessevdk/gtk,chergert/gtk,davidgumberg/gtk,ahodesuka/gtk,jadahl/gtk,chergert/gtk,alexlarsson/gtk,Lyude/gtk-,jadahl/gtk,Lyude/gtk-,Lyude/gtk-,jadahl/gtk,alexlarsson/gtk