Unregister listeners from ClockRegistry when destroyed am: e980bd3a5d am: 36c82537a1

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

Change-Id: I960d13a972ac0f5593e8ba71fe375005e0712bce
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>