Remove dead code: show_log() sep argument and diff_options.msg_sep

These variables were made unnecessary by commit
3969cf7db1.

Signed-off-by: Adam Simpkins <adam@adamsimpkins.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-log.c

@@ -770,7 +770,6 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	rev.diff = 1;
 	rev.combine_merges = 0;
 	rev.ignore_merges = 1;
-	rev.diffopt.msg_sep = "";
 	DIFF_OPT_SET(&rev.diffopt, RECURSIVE);
 
 	rev.subject_prefix = fmt_patch_subject_prefix;