Remove default impls from clock plugins am: 24ec252394 am: 54b9e9e57f

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

Change-Id: I89d9fbde2f15805246c8a3e40147c5c17bd3c66e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>