Invoices need to know what the peers' update contains, to create
routehints. It also wants to know if a peer has no other public
channels (so-called "dead end" peers) to eliminate them from routehint
consideration.
This was previously done by a special function to ask gossipd.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Temporarily rename old getroute to getrouteold (we will remove this).
Changelog-Changed: JSON-RPC: `getroute` is now implemented in a plugin.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>