Unfortunately, there appears to be no way to cancel a mapping request, so I've removed that function, and removed the return values used for cancelling. If cancelling comes back, it'll probably be in the form of a GCancellable anyway.

Compile only.
We removed implicit automatic port mapping when we replaced purple_proxy_connect with direct gio code. Protocols should probably be explicit about when they request a port mapping, but they haven't been made to do that yet.