Unregister listeners from ClockRegistry when destroyed am: e980bd3a5d am: efdddb1692

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

Change-Id: I10bf19040a5a739686badccde01364f356ea84c3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>