(PR#13839) PING, civmanual has been broken for ages

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=13839 >

Maybe not ages, but at least months. Without the patch that was
submitted four months ago, civmanual does not even start. Since nobody
seems to be using civmanual, it would perhaps be simpler to just
remove it from the repository.