ref_transaction_update(): remove "have_old" parameter

Instead, verify the reference's old value if and only if old_sha1 is
non-NULL.

ref_transaction_delete() will get the same treatment in a moment.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -252,7 +252,7 @@ static int fast_forward_to(const unsigned char *to, const unsigned char *from,
 	if (!transaction ||
 	    ref_transaction_update(transaction, "HEAD",
 				   to, unborn ? null_sha1 : from,
-				   0, 1, sb.buf, &err) ||
+				   0, sb.buf, &err) ||
 	    ref_transaction_commit(transaction, &err)) {
 		ref_transaction_free(transaction);
 		error("%s", err.buf);