builtin-remote.c: plug a small memory leak in get_one_remote_for_updates()

We know that the string pointed at by remote->name won't change.  It can
be borrowed as the key in the string_list without copying.  Other parts of
existing code such as get_one_entry() already rely on this fact.

Noticed by Cheng Renquan.

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

builtin-remote.c

@@ -770,7 +770,7 @@ static int get_one_remote_for_update(struct remote *remote, void *priv)
 {
 	struct string_list *list = priv;
 	if (!remote->skip_default_update)
-		string_list_append(xstrdup(remote->name), list);
+		string_list_append(remote->name, list);
 	return 0;
 }