Do we actually need the orconn_ext_or_id_map?

So apparently we have this structure, orconn_ext_or_id_map, where we map from ext_orport identifiers to the corresponding orconn objects ... but nothing in our code (outside of the unit tests) actually looks anything up in this map.

I can't remember -- is this a feature that we were planning to do something with if transports needed it in the future? Or is this just dead code?

Found while working on legacy/trac#33368 (moved).