HashLinkedList::Iterator: remove an ununsed class variable

Summary: This variable is not used. Remove it.

Test Plan: build.

Reviewers: haobo, igor, yhchiang

Reviewed By: haobo

CC: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18525

util/hash_linklist_rep.cc

@@ -259,7 +259,6 @@ class HashLinkListRep : public MemTableRep {
     const HashLinkListRep* const hash_link_list_rep_;
     Node* head_;
     Node* node_;
-    std::string tmp_;       // For passing to EncodeKey
 
     virtual void SeekToHead() {
       node_ = head_;