code: protected void fireKNNsRemoved(DBIDs removals, DBIDs updates) {
      KNNChangeEvent e = new KNNChangeEvent(this, KNNChangeEvent.Type.DELETE, removals, updates);
      Object[] listeners = listenerList.getListenerList();
      for(int i = listeners.length - 2; i >= 0; i -= 2) {
        if(listeners[i] == KNNListener.class) {
          ((KNNListener) listeners[i + 1]).kNNsChanged(e);
        }
      }
    }
docs: Informs all registered KNNListener that existing kNNs have been removed and
  as a result some kNNs have been changed.
  
  @param removals the ids of the removed kNNs
  @param updates the ids of kNNs which have been changed due to the removals
  @see KNNListener