arima constructor: remove spurious display

src/@arima/arima.m

@@ -2,7 +2,7 @@ classdef arima<handle % --*-- Unitary tests --*--
 
 % Class for ARIMA models (interface to X13).
 
-% Copyright (C) 2017 Dynare Team
+% Copyright (C) 2017-2022 Dynare Team
 %
 % This code is free software: you can redistribute it and/or modify
 % it under the terms of the GNU General Public License as published by
@@ -48,7 +48,6 @@ methods
         %
         % OUPUTS
         % - o      [arima]      ARIMA model object.
-        nargin
         switch nargin
           case 0
             % Return empty object.