openscenegraph: fix eval

pkgs/development/libraries/openscenegraph/default.nix

···
     homepage = http://www.openscenegraph.org/;
     maintainers = [ maintainers.raskin ];
     platforms = platforms.linux;
-    hydraPlatforms = lib.optionals (!withQt5) meta.platforms;
     license = "OpenSceneGraph Public License - free LGPL-based license";
   };
 }