Deprecate --gfe2_restart_flag_quic_return_error_on_empty_scid.

PiperOrigin-RevId: 499234880

quiche/quic/core/crypto/quic_crypto_server_config.cc

diff --git a/quiche/quic/core/crypto/quic_crypto_server_config.cc b/quiche/quic/core/crypto/quic_crypto_server_config.cc
index e2ee0eb..17cc94f 100644
--- a/quiche/quic/core/crypto/quic_crypto_server_config.cc
+++ b/quiche/quic/core/crypto/quic_crypto_server_config.cc
@@ -1610,12 +1610,10 @@
     QUIC_LOG(WARNING) << "Server config message is missing SCID";
     return nullptr;
   }
-  if (GetQuicRestartFlag(quic_return_error_on_empty_scid) && scid.empty()) {
-    QUIC_RESTART_FLAG_COUNT(quic_return_error_on_empty_scid);
+  if (scid.empty()) {
     QUIC_LOG(WARNING) << "Server config message contains an empty SCID";
     return nullptr;
   }
-  QUICHE_DCHECK(!scid.empty());
   config->id = std::string(scid);
 
   if (msg->GetTaglist(kAEAD, &config->aead) != QUIC_NO_ERROR) {

quiche/quic/core/quic_flags_list.h

diff --git a/quiche/quic/core/quic_flags_list.h b/quiche/quic/core/quic_flags_list.h
index 3dddf91..4232a21 100644
--- a/quiche/quic/core/quic_flags_list.h
+++ b/quiche/quic/core/quic_flags_list.h
@@ -19,8 +19,6 @@
 QUIC_FLAG(quic_reloadable_flag_quic_no_write_control_frame_upon_connection_close, true)
 // If true, QUIC will default enable MTU discovery at server, with a target of 1450 bytes.
 QUIC_FLAG(quic_reloadable_flag_quic_enable_mtu_discovery_at_server, false)
-// If true, QuicCryptoServerConfig::ParseConfigProtobuf will treat an empty SCID as the same as non-existent.
-QUIC_FLAG(quic_restart_flag_quic_return_error_on_empty_scid, true)
 // If true, QuicGsoBatchWriter will support release time if it is available and the process has the permission to do so.
 QUIC_FLAG(quic_restart_flag_quic_support_release_time_for_gso, false)
 // If true, ack frequency frame can be sent from server to client.