Remove default impls from clock plugins am: 24ec252394

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

Change-Id: Ibe4fd741a079eea90c841df9a8b5a17ab01b02cb
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>