Revert "tuna: dexopt /system apps to /cache"

This reverts commit 0836920f4372a70806c9c69cd966e985cf29670d.

Change-Id: Ic6531596513e958cccbeef787bdd139b77610d66
(cherry picked from commit a125136caf4737b1e06c5aba21e4257b0346b99a)