patch 8.2.3961: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/autocmd.c b/src/autocmd.c
index 94bd49a..4831ea8 100644
--- a/src/autocmd.c
+++ b/src/autocmd.c
@@ -580,7 +580,7 @@
     if (del_group)
     {
 	if (*arg == NUL)
-	    emsg(_(e_argreq));
+	    emsg(_(e_argument_required));
 	else
 	    au_del_group(arg);
     }