Fix test flakiness of SplashScreenExceptionListTest

The listener map of DeviceConfig uses OnPropertiesChangedListener
as key, so when iterating the map for dispatching change event,
the order may not be the same as the order of adding the listener.
Then the test may fail because the CountDownLatch counts before the
listener of SplashScreenExceptionList is called.

This change removes the additional test listener by overriding the
method which needs to be waited until it is called, which also
eliminates the dependency of listener callback order.

Fixes: 212660691
Test: atest SplashScreenExceptionListTest

Change-Id: I405932729d26f43428c70f5e282aeb8ae82d81c8