Remove get_bridge_pt_addrport().

The code was not disambiguating ClientTransportPlugin configured and
not used, and ClientTransportPlugin configured, but in a failed state.

The right thing to do is to undo moving the get_transport_by_addrport()
call back into get_proxy_addrport(), and remove and explicit check for
using a Bridge since by the time the check is made, if a Bridge is
being used, it is PT/proxy-less.