http-push: use in_merge_bases() for fast-forward check

The original computed merge-base between HEAD and the remote ref and
checked if the remote ref is a merge base between them, in order to
make sure that we are fast-forwarding.

Instead, call in_merge_bases(remote, HEAD) which does the same.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

http-push.c

@@ -1610,9 +1610,8 @@ static int verify_merge_base(unsigned char *head_sha1, struct ref *remote)
 {
 	struct commit *head = lookup_commit_or_die(head_sha1, "HEAD");
 	struct commit *branch = lookup_commit_or_die(remote->old_sha1, remote->name);
-	struct commit_list *merge_bases = get_merge_bases(head, branch, 1);
 
-	return (merge_bases && !merge_bases->next && merge_bases->item == branch);
+	return in_merge_bases(branch, head);
 }
 
 static int delete_remote_branch(const char *pattern, int force)