Currently if artifact is marked as deleted all
its blobs logicaly become 'pending_delete' and
can't be used anymore.
For this reason there is no need to have addtional
blob status and explicitely mark blobs - it's all
done when we change artifact status to 'deleted'
ApiImpact
Change-Id: Ide2bb3130d400b7ddcde0760246003b745ef4ff0