codec2: revert mark cross as broken (#414971)

pkgs/by-name/co/codec2/package.nix

···
     license = licenses.lgpl21Only;
     platforms = platforms.unix;
     maintainers = with maintainers; [ markuskowa ];
-    # generate_codebook only built for host platform
-    broken = !stdenv.buildPlatform.canExecute stdenv.hostPlatform;
     pkgConfigModules = [ "codec2" ];
   };
 })