removes a socket listener from liveQuery and also destroys the whole liveQuery if no more listeners are present
@param socket
function (socket) {
    if (this.listeners[socket.id]) {
      delete this.listeners[socket.id]
      if (Object.keys(this.listeners).length === 0) {
        this.destroy() // this will delete a liveQuery from liveQueries
      }
    } else {
      return new Error('no listener present on LQ ' + this.qKey)
    }
  }