fix: remove internal relay discovery

This logic collects a list of known relays by testing every new connection.

It exists so we can dial /p2p-circuit/p2p/QmFoobar addresses (circuit addresses
that don't specify the relay). However, this kind of address is useless outside
of basic demos as a random relay is practically guaranteed to not be connected
to the target peer. Picking a random relay to connect to some peer is almost
_never_ the desired behavior.

core/node/libp2p/relay.go

@@ -11,7 +11,7 @@ func Relay(disable, enableHop bool) func() (opts Libp2pOpts, err error) {
 			// Enabled by default.
 			opts.Opts = append(opts.Opts, libp2p.DisableRelay())
 		} else {
-			relayOpts := []relay.RelayOpt{relay.OptDiscovery}
+			relayOpts := []relay.RelayOpt{}
 			if enableHop {
 				relayOpts = append(relayOpts, relay.OptHop)
 			}