CleanupIteratorState() only to initialize DeletionState when super version cleanup needed

Summary:
Two changes:
1. DeletionState is only constructed when cleaning up is needed
2. Fix the bug of deletion state construction bug. A change was made in a previous patch: https://reviews.facebook.net/rROCKSDB774ed89c2405ee058086b099cbc8b29e243739cc#71a34e2e However, it somehow got lost when merging

Test Plan: make all check

Reviewers: kailiu, haobo, igor

Reviewed By: igor

CC: igor, dhruba, i.am.jin.lei, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D16233