code: func (*wsNotificationManager) removeSpentRequest(ops map[wire.OutPoint]map[chan struct{}]*wsClient,
  	wsc *wsClient, op *wire.OutPoint) {
  
  	// Remove the request tracking from the client.
  	delete(wsc.spentRequests, *op)
  
  	// Remove the client from the list to notify.
  	notifyMap, ok := ops[*op]
  	if !ok {
  		rpcsLog.Warnf("Attempt to remove nonexistent spent request "+
  			"for websocket client %s", wsc.addr)
  		return
  	}
  	delete(notifyMap, wsc.quit)
  
  	// Remove the map entry altogether if there are
  	// no more clients interested in it.
  	if len(notifyMap) == 0 {
  		delete(ops, *op)
  	}
  }
docs: // removeSpentRequest modifies a map of watched outpoints to remove the
  // websocket client wsc from the set of clients to be notified when a
  // watched outpoint is spent.  If wsc is the last client, the outpoint
  // key is removed from the map.