code: func (c *Cluster) Removed() []uint64 {
  	c.mu.RLock()
  	removed := make([]uint64, 0, len(c.removed))
  	for k := range c.removed {
  		removed = append(removed, k)
  	}
  	c.mu.RUnlock()
  	return removed
  }
docs: // Removed returns the list of raft Members removed from the Cluster.