Remove default impls from clock plugins am: 24ec2523 am: 54b9e9e5 am: 6d4c3f45 am: 4585494a

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/23438120



Change-Id: I7239f2be2353835a7ab0f3e7d8561b0ba9a4bff3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>