Revert dexopt to /cache

Squash of the following commits:

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

This reverts commit c44bb1e7e086884f30d41f64ee3b5cb4032253b5.

Revert "runtime: dexroot-on-cache: obey dalvik.vm.dexopt-data-only"

This reverts commit 236a8af22f7dac6bbffbf82701ae676148dc7d93.

Revert "runtime: Add support for dexroot-on-cache"

This reverts commit 135073693f6f4e233ac2eb665b3255f3bed44d26.

Change-Id: I7249239a66f107ad92499eb8bcd501ff8efbe300