Summary: It seems to me that when ever function MemTableRep::GetIterator(const Slice& slice) is used, we can use MemTableRep::GetDynamicPrefixIterator() instead. Just delete it to simplify the codes.
Test Plan: make all check
Reviewers: yhchiang, ljin
Reviewed By: ljin
Subscribers: xjin, dhruba, haobo, leveldb
Differential Revision: https://reviews.facebook.net/D19281