Deprecate gfe2_reloadable_flag_quic_postpone_discarding_zero_rtt_keys.

PiperOrigin-RevId: 339341964
Change-Id: I09aff6fb867e8148388e251c649ef1d79c35b639

quic/core/tls_client_handshaker.cc

diff --git a/quic/core/tls_client_handshaker.cc b/quic/core/tls_client_handshaker.cc
index 234b4d1..c38724b 100644
--- a/quic/core/tls_client_handshaker.cc
+++ b/quic/core/tls_client_handshaker.cc
@@ -400,14 +400,8 @@
   if (level == ENCRYPTION_FORWARD_SECURE || level == ENCRYPTION_ZERO_RTT) {
     encryption_established_ = true;
   }
-  const bool postpone_discarding_zero_rtt_keys =
-      GetQuicReloadableFlag(quic_postpone_discarding_zero_rtt_keys);
-  if (!postpone_discarding_zero_rtt_keys &&
-      level == ENCRYPTION_FORWARD_SECURE) {
-    handshaker_delegate()->DiscardOldEncryptionKey(ENCRYPTION_ZERO_RTT);
-  }
   TlsHandshaker::SetWriteSecret(level, cipher, write_secret);
-  if (postpone_discarding_zero_rtt_keys && level == ENCRYPTION_FORWARD_SECURE) {
+  if (level == ENCRYPTION_FORWARD_SECURE) {
     handshaker_delegate()->DiscardOldEncryptionKey(ENCRYPTION_ZERO_RTT);
   }
 }