lru/lru.go
func (c *LRU) RemoveOldest() (key string, value uint64, ok bool) {
	ent := c.evictList.Back()
	if ent != nil {
		c.removeElement(ent)
		kv := ent.Value.(*entry)
		return kv.key, kv.value, true
	}
	return "", 0, false
}
func (c *LRU) RemoveOldest() (key string, value uint64, ok bool) {
	ent := c.evictList.Back()
	if ent != nil {
		c.removeElement(ent)
		kv := ent.Value.(*entry)
		return kv.key, kv.value, true
	}
	return "", 0, false
}
// RemoveOldest removes the oldest item from the cache.