Use LeastUnacked to calculate the packet number length instead of GetLeastPacketAwaitedByPeer.

net/quic/core/quic_sent_packet_manager.cc

Index: net/quic/core/quic_sent_packet_manager.cc
diff --git a/net/quic/core/quic_sent_packet_manager.cc b/net/quic/core/quic_sent_packet_manager.cc
index 7dbf0a483cd5b8939ca43a20bf6c73bacdc4a21a..6c61884169abd39b985b22c14d53cb0acc26e995 100644
--- a/net/quic/core/quic_sent_packet_manager.cc
+++ b/net/quic/core/quic_sent_packet_manager.cc
@@ -986,6 +986,7 @@ QuicPacketNumber QuicSentPacketManager::GetLargestSentPacket(QuicPathId) const {
   return unacked_packets_.largest_sent_packet();
 }
 
+// Remove this method when deprecating QUIC_VERSION_33.
 QuicPacketNumber QuicSentPacketManager::GetLeastPacketAwaitedByPeer(
     QuicPathId) const {
   return least_packet_awaited_by_peer_;