don't over-expose private dependencies

Change-Id: I6045425fb467002db288854f9d0a8f8ea683876f
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

src/sensors/sensors.pro

@@ -7,7 +7,7 @@ CONFIG(debug,debug|release):DEFINES += ENABLE_RUNTIME_SENSORLOG
 
 qtHaveModule(simulator) {
     DEFINES += SIMULATOR_BUILD
-    QT += simulator
+    QT_FOR_PRIVATE += simulator
 }
 
 QMAKE_DOCS = $$PWD/doc/qtsensors.qdocconf