Revert "Add aidl::nullable type for nullable in AIDL" am: 9d1292e8e0 am: fdf65ac1fb am: 277d87a3ca

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/12334431

Change-Id: I9c0f7ae4bc78b9c2521f8d332e91c4de1f49bea3