Unregister listeners from ClockRegistry when destroyed am: e980bd3a5d

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

Change-Id: Iea54787e9f56d2e179c6879fb72ce8f60bb05b1f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>