Revert "Avoid internal APEX stubs for libsigchain and clean up e..." am: 5557553ae9 am: 45c45f6e07 am: 491ff05180

Original change: https://android-review.googlesource.com/c/platform/art/+/1660247

Change-Id: Icf6498f79ab84f35f15f760faa0d11a278786c41