patch 8.0.0281: some files are still using ARGSUSED instead of UNUSED

Problem:    MS-Windows files are still using ARGSUSED while most other files
            have UNUSED.
Solution:   Change ARGSUSED to UNUSED or delete it.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    281,
 /**/
     280,
 /**/