gfe-relnote: deprecate gfe2_reloadable_flag_quic_enable_pcc3

As http://b/64565089#comment31 says, there's no active work on PCC and there's
no sign that will change soon.

PiperOrigin-RevId: 307452986
Change-Id: If4fde03789c2783a5e9600ffc9feee1cf3183662

quic/core/congestion_control/send_algorithm_interface.cc

diff --git a/quic/core/congestion_control/send_algorithm_interface.cc b/quic/core/congestion_control/send_algorithm_interface.cc
index d7b2eca..9d003c5 100644
--- a/quic/core/congestion_control/send_algorithm_interface.cc
+++ b/quic/core/congestion_control/send_algorithm_interface.cc
@@ -45,12 +45,7 @@
               ? static_cast<BbrSender*>(old_send_algorithm)
               : nullptr);
     case kPCC:
-      if (GetQuicReloadableFlag(quic_enable_pcc3)) {
-        return CreatePccSender(clock, rtt_stats, unacked_packets, random, stats,
-                               initial_congestion_window,
-                               max_congestion_window);
-      }
-      // Fall back to CUBIC if PCC is disabled.
+      // PCC is work has stalled, fall back to CUBIC instead.
       QUIC_FALLTHROUGH_INTENDED;
     case kCubicBytes:
       return new TcpCubicSenderBytes(

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 3f290ae..5e672c1 100644
--- a/quic/core/quic_sent_packet_manager.cc
+++ b/quic/core/quic_sent_packet_manager.cc
@@ -215,9 +215,6 @@
              (GetQuicReloadableFlag(quic_default_to_bbr) &&
               config.HasClientRequestedIndependentOption(kQBIC, perspective))) {
     SetSendAlgorithm(kCubicBytes);
-  } else if (GetQuicReloadableFlag(quic_enable_pcc3) &&
-             config.HasClientRequestedIndependentOption(kTPCC, perspective)) {
-    SetSendAlgorithm(kPCC);
   }
 
   // Initial window.