This was added just so that moc could pick up the enums and so that
we could use the enums in Q_PROPERTY declarations, which was needed for
accessibility in QML. It turns out that Q_GADGET is enough for us.
This is a strictly a binary compatible change.
However, QAccessible was marked internal in 5.0, so we are free to
change it. In addition, this class is static and cannot be instantiated.
Change-Id: I27e2e97c5f4b45c38678264c6b593a4383db8d3e
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>