We changed the document deletion to use a manual WriteUnitOfWork, since we needed to leverage the onCommit handler to fulfill the completion promise. This was a temporary solution to
SERVER-54460. However, SERVER-54460 has been solved by instead adding setAlwaysInterruptAtStepDownOrUp to relevant opCtxs. We no longer need to onCommit handler.
As code cleanup we can convert resharding document deletion back to using the PersistentTaskStore, which uses fewer lines of code.