Removed support for unacknowledged writes in the WriteResult class that was deprecated in 2.12.0.

Additionally, all DBCollection methods that return a WriteResult will return null if the write was unacknowledged. If you need any of the properties of WriteResult, use acknowledged write concern, e.g. ACKNOWLEDGED, REPLICA_SAFE, etc.

If the write results in an error, methods that return a WriteResult with throw an exception.