Avoid use of private Qt API by dropping workaround in accessibleWidgetFactory

This condition is not mentioned in documentation or any examples for QAccessibleInterface, it was apparently copied from qtbase's qAccessibleFactory. That means it's most likely not necessary in plain applications, otherwise it would be done by Qt itself.

I tested this with at-spi2 + orca in an X11 Plasma session, I couldn't find any difference regarding the "Audit Log" label and it did not crash.