The singular outgoing_chan_id query parameter on LND's QueryRoutes is
deprecated as of lnd 0.20.0 in favor of the plural outgoing_chan_ids.
The code path was unreachable in RTL anyway: no caller of the
GetQueryRoutes action ever populated outgoingChanId, so the query
parameter was never sent. Drop the unused field, the effect's
conditional URL builder, and the server-side passthrough.