Revert dexopt to /cache

Squash of the following commits:

Revert "installd: Invert the default for dexopt-on-cache"

This reverts commit d018d2ecb3ee31bc549e6b43f8e6b5564569d63a.

Revert "DexOpt anything on /system in /cache/dalvik-cache"

This reverts commit 4ff8448cc41eea749e59b316e456777b3d9ca1ed.

Change-Id: I7249239a66f107ad92499eb8bcd501ff8efbe300