SDL_ttf: don't link itself to /include

pkgs/development/libraries/SDL_ttf/default.nix

···
 
   buildInputs = [ SDL freetype ];
 
-  postInstall = "ln -s $out/include/SDL/SDL_ttf.h $out/include/";
-
   meta = with stdenv.lib; {
     description = "SDL TrueType library";
     license = licenses.zlib;