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

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

Change-Id: I8500fbe24a9ab75b8e8b6eaf0e074e1955582208