deleteValue method
Updates one NodeValueObject with a new NodeValueObject by copying all fields except key.
The key is used to search the NodeValueObject to update.
@param path the path to the node @param key the key to be removed from the value @return the removed node value @throws StorageException if the storage backend encounters a problemImplementation
@override
Future<NodeValue> deleteValue(String nodeName, String key) async {
await _finishInit();
return await _deleteValue(nodeName, key);
}