Remove multipath_enabled from quic_config and quic_connection. No functional change expected.

net/quic/test_tools/quic_connection_peer.cc

Index: net/quic/test_tools/quic_connection_peer.cc
diff --git a/net/quic/test_tools/quic_connection_peer.cc b/net/quic/test_tools/quic_connection_peer.cc
index 344013c5c2eb94a2d250fa31ae868d47168bc21b..d96b991425e1c5dae19f524995ce9637537eabb5 100644
--- a/net/quic/test_tools/quic_connection_peer.cc
+++ b/net/quic/test_tools/quic_connection_peer.cc
@@ -104,11 +104,6 @@ bool QuicConnectionPeer::IsSilentCloseEnabled(QuicConnection* connection) {
 }
 
 // static
-bool QuicConnectionPeer::IsMultipathEnabled(QuicConnection* connection) {
-  return connection->multipath_enabled_;
-}
-
-// static
 void QuicConnectionPeer::SwapCrypters(QuicConnection* connection,
                                       QuicFramer* framer) {
   QuicFramerPeer::SwapCrypters(framer, &connection->framer_);