Unregister listeners from ClockRegistry when destroyed am: e980bd3a5d am: 36c82537a1 am: 9451731a26 am: 071e6583a1

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/23407197

Change-Id: I4cdfed5bc9c2b39c370bd70df628399b9b53ac2e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>