Deprecate gfe2_reloadable_flag_quic_use_half_rtt_as_first_pto.

PiperOrigin-RevId: 331577686
Change-Id: Ic4fd8f68e24b6e5cf9b99aec87ad384c2fc70a15

quic/core/quic_sent_packet_manager.cc

diff --git a/quic/core/quic_sent_packet_manager.cc b/quic/core/quic_sent_packet_manager.cc
index 91e119a..930b4ed 100644
--- a/quic/core/quic_sent_packet_manager.cc
+++ b/quic/core/quic_sent_packet_manager.cc
@@ -1258,10 +1258,8 @@
                QuicTime::Delta::FromMilliseconds(kMinHandshakeTimeoutMs)) *
            (1 << consecutive_pto_count_);
   }
-  if (GetQuicReloadableFlag(quic_use_half_rtt_as_first_pto) &&
-      enable_half_rtt_tail_loss_probe_ && consecutive_pto_count_ == 0 &&
+  if (enable_half_rtt_tail_loss_probe_ && consecutive_pto_count_ == 0 &&
       handshake_finished_) {
-    QUIC_RELOADABLE_FLAG_COUNT(quic_use_half_rtt_as_first_pto);
     return std::max(min_tlp_timeout_, rtt_stats_.smoothed_rtt() * 0.5);
   }
   const QuicTime::Delta rtt_var = use_standard_deviation_for_pto_

quic/core/quic_sent_packet_manager_test.cc

diff --git a/quic/core/quic_sent_packet_manager_test.cc b/quic/core/quic_sent_packet_manager_test.cc
index 3187d7c..29ea106 100644
--- a/quic/core/quic_sent_packet_manager_test.cc
+++ b/quic/core/quic_sent_packet_manager_test.cc
@@ -4141,7 +4141,6 @@
 }
 
 TEST_F(QuicSentPacketManagerTest, PtoWithTlpr) {
-  SetQuicReloadableFlag(quic_use_half_rtt_as_first_pto, true);
   QuicConfig config;
   QuicTagVector options;