merge: don't document non-existing --compact-summary argument

3a54f5b (merge/pull: add the "--compact-summary" option, 2025-06-12)
added the option --compact-summary to both merge and pull.  It takes no
no argument, but for merge it got an argument help string.  Remove it,
since it is unnecessary.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: rscharfe

builtin/merge.c

@@ -264,7 +264,7 @@ static struct option builtin_merge_options[] = {
 	OPT_BOOL(0, "stat", &show_diffstat,
 		N_("show a diffstat at the end of the merge")),
 	OPT_BOOL(0, "summary", &show_diffstat, N_("(synonym to --stat)")),
-	OPT_CALLBACK_F(0, "compact-summary", &show_diffstat, N_("compact-summary"),
+	OPT_CALLBACK_F(0, "compact-summary", &show_diffstat, NULL,
 		       N_("show a compact-summary at the end of the merge"),
 		       PARSE_OPT_NOARG,
 		       option_parse_compact_summary),