build-sys: remove GTK_DISABLE_DEPRECATED
build-sys: remove GTK_DISABLE_DEPRECATED

Gtk 3.0 no longer includes deprecated headers if it's defined:
http://git.gnome.org/browse/gtk+/commit/?id=a1de67f438f057711353a55b322babce7044226f

We added it as a workaround for Gtk 2.0 build issue.

Fantu/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,fgouget/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,flexVDI/spice-gtk,Fantu/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,fgouget/spice-gtk,elmarco/spice-gtk,fgouget/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,Fantu/spice-gtk,Fantu/spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,guodong/spice-gtk,flexVDI/spice-gtk