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.
diff --git a/src/version.c b/src/version.c
index 08e32cf..ef4a45f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    281,
+/**/
     280,
 /**/
     279,