diff-merges: get rid of now empty diff_merges_init_revs()

After getting rid of 'ignore_merges' field, the diff_merges_init_revs()
function became empty. Get rid of it.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-merges.c

@@ -21,10 +21,6 @@ static void set_dense_combined(struct rev_info *revs)
  * Public functions. They are in the order they are called.
  */
 
-void diff_merges_init_revs(struct rev_info *revs)
-{
-}
-
 int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 {
 	int argcount = 1;