Document that the QSensor constructor should not be used directly

Change-Id: I1907497b2bb3b1be65e98223e0337eef358743b6
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>
Remove debug output.

Task-number: QTBUG-31074

Change-Id: I7cb66ccbe74203e87e3bcc60400a8f7b2b2be0ed
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>