Unregister listeners from ClockRegistry when destroyed am: e980bd3a5d am: 29920aef25

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

Change-Id: Ia180e6dafedf80abc8980a61a539e2d422d74745
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>