Remove `conn_type`

[flub]

This is already being removed as part of the #3614 and #3610 work IIRC. But this needs to be removed somehow so let's have an issue for it.

[eminence]

Is there going to be a replacement for this? I use conn_type in dumbpipe to give some hints about if the connection is a direct connection or a relayed connection.

I recognize that multipath complicates this. I guess instead there might be some type of watcher/iterator over all the known paths (along with their connection type and maybe RTT) ?

[flub]

@eminence yes, the linked PRs in the above message are working on providing an API that can be used for this. A workable-subset of this has already landed in the feat-multipath branch itself. (We do need that functionality for tests too!).

[dignifiedquire]

This was done in #3647