We only support version 4 and 5 in Qt 6.0. 1 and 2 are already gone
(due to being based on binary JSON), now we remove 3 as well.
Task-number: QTBUG-81346
Change-Id: I3627dcc0587f1e36f11e93edf7172889e911d64e
Reviewed-by: Andy Nichols <andy.nichols@qt.io>