Obsolete AA_ImmediateWidgetCreation.

This attribute is not guaranteed to fully work with QPA.

Task-number: QTBUG-36489
Change-Id: I638a8e00851288012be553b5316aa6088dd67cff
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>