rip out PortForwarding options

A relay operator on tor-relays@ just got snookered into setting PortForwarding to 1, probably because he thought it would help him get port forwarding working on his relay.

I think the reality is that almost nobody uses this option, and also we don't recommend it.

Yawning rewrote the crappy dangerous C upnp apps in go: https://gitweb.torproject.org/tor.git/tree/src/tools/tor-fw-helper/README https://gitweb.torproject.org/tor-fw-helper.git/tree/README.md

But I don't think we've taken any steps to get that go version into any user's hands.

Also, our past use case, where Vidalia would launch Tor and want to let ordinary users turn themselves into relays or bridges, is long deprecated.

Alternatives to "rip it out" would be "get yawning's go stuff packaged properly in Debian", or "add yawning's go stuff to the tor tarball and build it and ship it too".

See also #21765 (moved) and its great phrase "I wonder how long this has been broken for".