code: func (xft *XFastTrie) Delete(keys ...uint64) {
  	for _, key := range keys {
  		xft.delete(key)
  	}
  }
docs: // Delete will delete the provided keys from the trie.  If an entry
  // associated with a provided key cannot be found, that deletion is
  // a no-op.  Each deletion is an O(log M) operation.