Problem:

When an update operation moved an externally stored LOB to an
inline stored data, then the old LOB was not marked as purgeable.
Because of this the purge thread was not freeing the old LOB
data.

Solution:

Identify such updates and mark the LOB appropriately so that
purge can free them.

rb#22825 approved by Kuba Lopuszanski <jakub.lopuszanski@oracle.com>