code: func (cs *clientStore) removeSub(ID string, sub *subState) bool {
  	cs.RLock()
  	defer cs.RUnlock()
  	c := cs.clients[ID]
  	if c == nil {
  		return false
  	}
  	c.Lock()
  	removed := false
  	c.subs, removed = sub.deleteFromList(c.subs)
  	c.Unlock()
  	return removed
  }
docs: // RemoveSub removes the subscription from the client identified by clientID
  // and returns true only if the client has not been unregistered and that
  // the subscription was found, otherwise returns false.