nixos/games: remove steam runtime nix-ld

`steam-run`'s fhsenv was refactored, and we should avoid relying on its
internal details anyway.

It seems like heroic no longer needs additional libraries anyway, but if
it did we could override its `extraLibraries` argument.

modules/nixos/games.nix

@@ -16,13 +16,8 @@ in
       ];
     };
 
-    programs.nix-ld = {
-      enable = true;
-      libraries = pkgs.steam-run.fhsenv.args.multiPkgs pkgs;
-    };
-
     environment.systemPackages = with pkgs; [
-      heroic
+      heroic # TODO: override extraLibraries ?
       prismlauncher
       steam-run
     ];