Removes the current sub-key and attempts to set the position to the sub-key after the removed one. If no such sub-key exists, the position will be the parent key in the traversal stack. Given the sub-key having position "N" in the traversal stack, the removal will always take place from position "N-1."
int KvDeleteThis(Handle kv)
1 if removal succeeded and there was another key. 0 if the current node was not contained in the previous node, or no previous node exists. -1 if removal succeeded and there were no more keys, thus the state is as if KvGoBack() was called.