Plug the code performing the actual range deletion at this point of the range deleter service.

• Create an operation context, similar to the way it's done here.
• Invoke uassertStatusOK(deleteRangeInBatches) (it is expected to fail only in case of stepdown or if the collection gets dropped)
• Replace the manual task deregistration with the deletion of the range deletion task document (the observer will then trigger the deregistration once the deletion is majority committed)