Revert "DO NOT MERGE ART: Turn off duplicate-classes checking"

This reverts commit aafcfca5fe545365ef377fff2897b8a908f03e71.

Bug: 21333911

(cherry picked from commit 18a1827a159f1b235f3fcc934f428059185f550e)

Change-Id: Ibbc6b1be8bebc1d0ab9c5955b34eb89f40577baa
2 files changed