So we don't have to maintain the requirements in two places.
None of the variables removed from the qmake configs are
referenced before we do load(qt_config), so this should
be safe.
Pick-to: 6.7
Change-Id: Iabd5884a2fd1c4b1cd7b44416bebb2624050229e
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>