tst_qnetworkproxyfactory: Fix warnings about unused variables.

Change-Id: I6fa08353ebea5cdd7fc7a0c982bf1b9d34bbc077
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>

tests/auto/network/kernel/qnetworkproxyfactory/tst_qnetworkproxyfactory.cpp

@@ -389,6 +389,11 @@ void tst_QNetworkProxyFactory::genericSystemProxy()
     QCOMPARE(systemProxy.first().port(), static_cast<quint16>(port));
     qunsetenv(envVar);
 #else
+    Q_UNUSED(envVar)
+    Q_UNUSED(url)
+    Q_UNUSED(proxyType)
+    Q_UNUSED(hostName)
+    Q_UNUSED(port)
     QSKIP("Generic system proxy not available on this platform.");
 #endif
 }