Remove unused member variables. No functional change.

net/quic/congestion_control/tcp_cubic_sender.cc

Index: net/quic/congestion_control/tcp_cubic_sender.cc
diff --git a/net/quic/congestion_control/tcp_cubic_sender.cc b/net/quic/congestion_control/tcp_cubic_sender.cc
index ac114d8ef7bcf87327239944f716801dcd4e62ef..81da996628cfd4422c28a87a25b824f827ececc8 100644
--- a/net/quic/congestion_control/tcp_cubic_sender.cc
+++ b/net/quic/congestion_control/tcp_cubic_sender.cc
@@ -48,8 +48,7 @@ TcpCubicSender::TcpCubicSender(const QuicClock* clock,
       min4_mode_(false),
       slowstart_threshold_(max_tcp_congestion_window),
       last_cutback_exited_slowstart_(false),
-      max_tcp_congestion_window_(max_tcp_congestion_window),
-      clock_(clock) {}
+      max_tcp_congestion_window_(max_tcp_congestion_window) {}
 
 TcpCubicSender::~TcpCubicSender() {
   UMA_HISTOGRAM_COUNTS("Net.QuicSession.FinalTcpCwnd", congestion_window_);