Remove default impls from clock plugins am: 24ec252394 am: 54b9e9e57f am: 6d4c3f450c

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

Change-Id: I1ab34673ff787ac13a299724e60ca85fa4214d3d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>