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

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

Change-Id: Ie6f33f0a6b2fd5a4fc994fefa84963c8cb1e644e