revert: Hide '-r' option in default usage

The '-r' command-line option is a no-op provided only for backward
compatiblity since abd6970 (cherry-pick: make -r the default, 2006-10-05),
and somehow ended up surviving across reimplementation in C at 9509af6
(Make git-revert & git-cherry-pick a builtin, 2007-03-01) and another
rewrite of the command line parser at f810379 (Make builtin-revert.c use
parse_options, 2007-10-07).  We should have stopped advertising the option
long time ago.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/revert.c

@@ -76,7 +76,8 @@ static void parse_args(int argc, const char **argv)
 	struct option options[] = {
 		OPT_BOOLEAN('n', "no-commit", &no_commit, "don't automatically commit"),
 		OPT_BOOLEAN('e', "edit", &edit, "edit the commit message"),
-		OPT_BOOLEAN('r', NULL, &noop, "no-op (backward compatibility)"),
+		{ OPTION_BOOLEAN, 'r', NULL, &noop, NULL, "no-op (backward compatibility)",
+		  PARSE_OPT_NOARG | PARSE_OPT_HIDDEN, NULL, 0 },
 		OPT_BOOLEAN('s', "signoff", &signoff, "add Signed-off-by:"),
 		OPT_INTEGER('m', "mainline", &mainline, "parent number"),
 		OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),