code: func (c *RPCClient) deregisterHandler(seq uint64) {
  	c.dispatchLock.Lock()
  	seqH, ok := c.dispatch[seq]
  	delete(c.dispatch, seq)
  	c.dispatchLock.Unlock()
  
  	if ok {
  		seqH.Cleanup()
  	}
  }
docs: // deregisterHandler is used to deregister a handler