I have observed that the next hard deletion timeout is not scheduled if
the `hardDeleteOnPruningCycle` function throws when fetching the data
from the database. That is because the thrown error is not caught and
the `scheduleHardDeletion` method is not called.
This PR moves the call to `scheduleHardDeletion` into the
`scheduleHardDeletion` for better cohesion, and ensures that it is
called even if `hardDeleteOnPruningCycle` throws.