Remove support for duplicate file entries

Summary:
Bug: 8219321
Change-Id: Ibc56bea753917c38e1bb20df48aa45fdff39d364

Test Plan: Works for me here, fixes the "99%" security "exploit." Someone else should test as well.

Reviewers: Mustaavalkosta, michyprima, rlasalle15, randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D204