p2p/discv5: add deprecation warning and remove unused code (#20367)

* p2p/discv5: add deprecation warning and remove unused code

* p2p/discv5: remove unused variables

p2p/discv5/sim_test.go

@@ -294,15 +294,6 @@ func (s *simulation) launchNode(log bool) *Network {
 	return net
 }
 
-func (s *simulation) dropNode(id NodeID) {
-	s.mu.Lock()
-	n := s.nodes[id]
-	delete(s.nodes, id)
-	s.mu.Unlock()
-
-	n.Close()
-}
-
 type simTransport struct {
 	joinTime   time.Time
 	sender     NodeID
@@ -358,22 +349,6 @@ func (st *simTransport) sendPing(remote *Node, remoteAddr *net.UDPAddr, topics [
 	return hash
 }
 
-func (st *simTransport) sendPong(remote *Node, pingHash []byte) {
-	raddr := remote.addr()
-
-	st.sendPacket(remote.ID, ingressPacket{
-		remoteID:   st.sender,
-		remoteAddr: st.senderAddr,
-		hash:       st.nextHash(),
-		ev:         pongPacket,
-		data: &pong{
-			To:         rpcEndpoint{IP: raddr.IP, UDP: uint16(raddr.Port), TCP: 30303},
-			ReplyTok:   pingHash,
-			Expiration: uint64(time.Now().Unix() + int64(expiration)),
-		},
-	})
-}
-
 func (st *simTransport) sendFindnodeHash(remote *Node, target common.Hash) {
 	st.sendPacket(remote.ID, ingressPacket{
 		remoteID:   st.sender,