builtin/send-pack: fix leaking refspecs

We never free data associated with the assembled refspec in
git-send-pack(1), causing a memory leak. Fix this.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/send-pack.c

@@ -338,5 +338,6 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
 
 	free_refs(remote_refs);
 	free_refs(local_refs);
+	refspec_clear(&rs);
 	return ret;
 }