Remove SmartSpaceComplication when the SmartspaceTargetListener is removed.

The listener removes the SmartSpaceComplication when the targets becomes
empty. If the listener isn't connected, we don't know whether/when the
targets becomes empty. Therefore we should just remove the complication
when the listener is removed.

This fixes the extra DATE card impression on the Dream surface. The
CardPagerAdapter adds a default DATE card when its setTargets method is
called with an empty list. This CL ensures that for Dream Smartspace,
the setTargets method is never called with an empty list.

Reorganized the existing testAvailability() test into multiple tests.
The new logic is tested in
testOverlayInActive_removesTargetListener_removesComplication().

Bug: 231251252
Test: on device via `adb logcat ...`
Test: atest SmartSpaceComplicationTest
Change-Id: Iac0d8a9697f42e2c70c83c5da050f17190fcc3c1