ackhandler: remove unneeded SetHandshakeConfirmed from SentPacketHandler (#4890)

According to section 4.9.2 of RFC 9001, dropping the Handshake packet
number spaces happens when the handshake is confirmed.

internal/ackhandler/interfaces.go

@@ -17,7 +17,6 @@ type SentPacketHandler interface {
 	ReceivedBytes(_ protocol.ByteCount, rcvTime time.Time)
 	DropPackets(_ protocol.EncryptionLevel, rcvTime time.Time)
 	ResetForRetry(rcvTime time.Time)
-	SetHandshakeConfirmed(now time.Time)
 
 	// The SendMode determines if and what kind of packets can be sent.
 	SendMode(now time.Time) SendMode

internal/ackhandler/sent_packet_handler.go

@@ -179,6 +179,9 @@ func (h *sentPacketHandler) DropPackets(encLevel protocol.EncryptionLevel, now t
 	case protocol.EncryptionInitial:
 		h.initialPackets = nil
 	case protocol.EncryptionHandshake:
+		// Dropping the handshake packet number space means that the handshake is confirmed,
+		// see section 4.9.2 of RFC 9001.
+		h.handshakeConfirmed = true
 		h.handshakePackets = nil
 	case protocol.Encryption0RTT:
 		// This function is only called when 0-RTT is rejected,
@@ -912,16 +915,3 @@ func (h *sentPacketHandler) ResetForRetry(now time.Time) {
 	}
 	h.ptoCount = 0
 }
-
-func (h *sentPacketHandler) SetHandshakeConfirmed(now time.Time) {
-	if h.initialPackets != nil {
-		panic("didn't drop initial correctly")
-	}
-	if h.handshakePackets != nil {
-		panic("didn't drop handshake correctly")
-	}
-	h.handshakeConfirmed = true
-	// We don't send PTOs for application data packets before the handshake completes.
-	// Make sure the timer is armed now, if necessary.
-	h.setLossDetectionTimer(now)
-}

internal/ackhandler/sent_packet_handler_test.go

@@ -133,7 +133,6 @@ var _ = Describe("SentPacketHandler", func() {
 	setHandshakeConfirmed := func() {
 		handler.DropPackets(protocol.EncryptionInitial, time.Now())
 		handler.DropPackets(protocol.EncryptionHandshake, time.Now())
-		handler.SetHandshakeConfirmed(time.Now())
 	}
 
 	Context("registering sent packets", func() {