Deprecate FLAGS_quic_allow_server_address_change_for_mapped_ipv4.

net/quic/core/quic_connection.cc

Index: net/quic/core/quic_connection.cc
diff --git a/net/quic/core/quic_connection.cc b/net/quic/core/quic_connection.cc
index ab062022b85958c3072a8ffb6abd92a92a83712e..9342a66da4a880b676390130f4c18eb7798a0315 100644
--- a/net/quic/core/quic_connection.cc
+++ b/net/quic/core/quic_connection.cc
@@ -1421,12 +1421,6 @@ bool QuicConnection::ProcessValidatedPacket(const QuicPacketHeader& header) {
       IsInitializedIPEndPoint(self_address_) &&
       IsInitializedIPEndPoint(last_packet_destination_address_) &&
       (!(self_address_ == last_packet_destination_address_))) {
-    if (!FLAGS_quic_allow_server_address_change_for_mapped_ipv4) {
-      CloseConnection(QUIC_ERROR_MIGRATING_ADDRESS,
-                      "Self address migration is not supported at the server.",
-                      ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-      return false;
-    }
     // Allow change between pure IPv4 and equivalent mapped IPv4 address.
     IPAddress self_ip = self_address_.address();
     if (self_ip.IsIPv4MappedIPv6()) {