llama-cpp: remove required models or modelsDir assertion

  };

  config = lib.mkIf cfg.enable {

    # Enforce that either model or modelDir is set

    assertions = [

      {

        assertion = cfg.model != null || cfg.modelsDir != null;

        message = "services.llama-cpp: Either 'model' or 'modelDir' must be set.";

      }

    ];

    systemd.services.llama-cpp = {

      description = "LLaMA C++ server";

      after = [ "network.target" ];