log: drop "--cc implies -m" logic

This was added by 82dee4160c (log: show merge commit when --cc is given,
2015-08-20), which explains why we need it. But that commit failed to
notice that setup_revisions() already does the same thing, since
cd2bdc5309 (Common option parsing for "git log --diff" and friends,
2006-04-14).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -731,10 +731,6 @@ static void log_setup_revisions_tweak(struct rev_info *rev,
 	/* Turn --cc/-c into -p --cc/-c when -p was not given */
 	if (!rev->diffopt.output_format && rev->combine_merges)
 		rev->diffopt.output_format = DIFF_FORMAT_PATCH;
-
-	/* Turn -m on when --cc/-c was given */
-	if (rev->combine_merges)
-		rev->ignore_merges = 0;
 }
 
 int cmd_log(int argc, const char **argv, const char *prefix)