qmljs: do not warn for QT_TR* functions

Change-Id: If5cf78434458ae639b4ebd0cb156110b5a291613
Task-number: QTCREATORBUG-12494
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>