Minor cleanup in tst_qnetworkreply

Remove using namespace std::chrono literals from httpConnectionCount,
it is already included at the top of the file.

Change-Id: I2dd748735a26a173c7a7361b313b87668a6fd805
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

tests/auto/network/access/qnetworkreply/tst_qnetworkreply.cpp

@@ -6682,7 +6682,6 @@ void tst_QNetworkReply::httpConnectionCount()
 
     int pendingConnectionCount = 0;
 
-    using namespace std::chrono_literals;
     const auto newPendingConnection = [&server]() { return server->hasPendingConnections(); };
     // If we have http2 enabled then the second connection will take a little
     // longer to be established because we will wait for the first one to finish