client/authority-discovery: Don't add own address to priority group (#6370)

* client/authority-discovery: Don't add own address to priority group

In the scenario of a validator publishing the address of its sentry node
to the DHT, said sentry node should not add its own Multiaddr to the
peerset "authority" priority group.

Related to 273f31b7.

* client/authority-discovery: Remove unused import PeerId

* client/authority-discovery/tests: Add tcp protocol to multiaddresses