Revert "castxml: mark as broken on Darwin"

The package was marked as broken on master, but is fixed in this
iteration of staging.

This reverts commit d5eaacf7db.

pkgs/development/tools/castxml/default.nix

@@ -64,6 +64,5 @@ stdenv.mkDerivation rec {
     license = licenses.asl20;
     maintainers = with maintainers; [ AndersonTorres ];
     platforms = platforms.unix;
-    broken = stdenv.isDarwin;
   };
 }