Fix warnings about unused variables in benchmarks

This patch removes two unused variables and marks one unused, fixing
three warnings.

Change-Id: I71f59839452590b82ffb5459a968f06bd434fb9a
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

tests/benchmarks/corelib/tools/containers-associative/main.cpp

@@ -111,6 +111,7 @@ void testLookup(int size)
             val = container.value(i);
 
     }
+    Q_UNUSED(val);
 }
 
 void tst_associative_containers::lookup()

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

@@ -233,7 +233,6 @@ class ThreadedDataReaderHttpServer: public QThread
     // used to make the constructor only return after the tcp server started listening
     QSemaphore ready;
     QTcpSocket *client;
-    int timeout;
     int port;
 public:
     qint64 transferRate;

tests/benchmarks/widgets/graphicsview/qgraphicslayout/tst_qgraphicslayout.cpp

@@ -114,8 +114,6 @@ void tst_QGraphicsLayout::invalidate()
 
     // ...then measure...
 
-    int pass = 1;
-
     // should be as small as possible, to reduce overhead of painting
     QSizeF size(1, 1);
     setGeometryCalls->clear();