refactor(users): set mutableUsers in sydnix.users

hosts/sydpc/configuration.nix

@@ -121,17 +121,12 @@
     pkgs.cachix
   ];
 
-  programs.xwayland.enable = true;
-
   services.openssh = {
     enable = true;
     settings.PermitRootLogin = "yes";
     settings.X11Forwarding = true;
   };
 
-  # TODO: Move to defaults.
-  users.mutableUsers = false;
-
   nix = {
     settings = {
       allow-import-from-derivation = true;