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/net.go

@@ -77,14 +77,6 @@ type Network struct {
 	nursery       []*Node
 	nodes         map[NodeID]*Node // tracks active nodes with state != known
 	timeoutTimers map[timeoutEvent]*time.Timer
-
-	// Revalidation queues.
-	// Nodes put on these queues will be pinged eventually.
-	slowRevalidateQueue []*Node
-	fastRevalidateQueue []*Node
-
-	// Buffers for state transition.
-	sendBuf []*ingressPacket
 }
 
 // transport is implemented by the UDP transport.
@@ -104,10 +96,9 @@ type transport interface {
 }
 
 type findnodeQuery struct {
-	remote   *Node
-	target   common.Hash
-	reply    chan<- []*Node
-	nresults int // counter for received nodes
+	remote *Node
+	target common.Hash
+	reply  chan<- []*Node
 }
 
 type topicRegisterReq struct {
@@ -650,10 +641,10 @@ loop:
 	if net.conn != nil {
 		net.conn.Close()
 	}
-	if refreshDone != nil {
-		// TODO: wait for pending refresh.
-		//<-refreshResults
-	}
+	// TODO: wait for pending refresh.
+	// if refreshDone != nil {
+	// 	<-refreshResults
+	// }
 	// Cancel all pending timeouts.
 	for _, timer := range net.timeoutTimers {
 		timer.Stop()