nixos/systemd-sysusers: remove assertion

        assertion = config.system.activationScripts.users == "";

        message = "system.activationScripts.users has to be empty to use systemd-sysusers";

      }

      {

        assertion = config.users.mutableUsers -> config.system.etc.overlay.enable;

        message = "config.users.mutableUsers requires config.system.etc.overlay.enable.";

      }

    ] ++ (lib.mapAttrsToList

      (username: opts: {

        assertion = !opts.isNormalUser;