Remove default impls from clock plugins am: 24ec252394 am: 54b9e9e57f am: ac3c2f90df am: 3af608fef1

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

Change-Id: If9c6e49e48e2bef4d3def7b73116fc1071099239
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>