Remove unused empty structs in libscelt.
Remove unused empty structs in libscelt.

SuperTux88/sbcelt,mkrautz/sbcelt,mumble-voip/sbcelt,SuperTux88/sbcelt,SuperTux88/sbcelt,mumble-voip/sbcelt,mumble-voip/sbcelt,mkrautz/sbcelt,SuperTux88/sbcelt,mumble-voip/sbcelt,mkrautz/sbcelt,mkrautz/sbcelt