When LRUCache insert and evict a large number of entries, there are
frequently calls of HandleTable::remove(e->key, e->hash), it will
lookup the entry in the hash table. Now that we know the entry to
remove 'e', we can remove it directly from hash table's collision list
if it's a double linked list.
This patch refactor the collision list to double linked list, the simple
benchmark CacheTest.SimpleBenchmark shows that time cost reduced about
18% in my test environment.
