Major Description
DELETESHARD only cleans up the index directory and not the instance/data directory. DELETEREPLICA on the other hand cleans up the data and instance directory.
DELETESHARD should clean up the instance and data directory, so that we don't leak disk space on executing the command.
If we think this would break back-compat, though I don't see why this should not clean up the instance dir, we should at least provide an option to clean up everything and make it default in 6.0.