message: Remove unused mockStats_ from QuicServerTest
  Summary: can't see where it's used.
diff: @@ -1847,7 +1847,6 @@ class QuicServerTest : public Test {
  EXPECT_CALL(*transport, setTransportStatsCallback(nullptr));
  EXPECT_CALL(*transport, setRoutingCallback(nullptr));
  EXPECT_CALL(*transport, closeNow(_));
  - mockStats_.reset();
  server_->shutdown();
  closeUdpClient(std::move(client));
  // cleanup transport
  @@ -1863,7 +1862,6 @@ class QuicServerTest : public Test {
  MockQuicServerTransportFactory* factory_;
  TransportSettings transportSettings_;
  MockQuicStatsFactory* transportStatsFactory_;
  - folly::ThreadLocalPtr<MockQuicStats> mockStats_;
  uint32_t clientHostId_{0}, serverHostId_{0xAABBCC};
  }; // namespace test
  