We should mention in its doc comment that https://github.com/Islandora/islandora/blob/7.x/islandora.module#L1260 is preferred.  Another consideration is that https://github.com/Islandora/islandora/blob/7.x/islandora.module#L1260 is called 'delete' while the actual action is purge. If it's a concern we should deprecate for a new signature.