Summary:
This diff basically reverts D30249 and also adds a unit test that was failing before this patch.

I have no idea how I didn't catch this terrible bug when writing a diff, sorry about that :(

I think we should redesign our system of keeping track of and deleting files. This is already a second bug in this critical piece of code. I'll think of few ideas.

BTW this diff is also a regression when running lots of column families. I plan to revisit this separately.

Test Plan: added a unit test

Reviewers: yhchiang, rven, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D33045