win32/ifchange.bat: Discard useless message

When the destination does not exist, `del` needs to do nothing.

Author: nobu

win32/ifchange.bat

@@ -89,7 +89,7 @@ if exist %dest% (
     )
 )
 for %%I in (%1) do echo %%~I updated
-del /f %dest%
+del /f %dest% 2> nul
 copy %src% %dest% > nul
 del %src%