Clean-up brightness configuration.

Remove unused default config since that's now stored in the mapping
strategy and eliminate erroneous error logging on devices that don't
support brightness configurations.

Fixes: 71527790
Test: atest com.android.server.display.BrightnessMappingStrategyTest
Change-Id: I9b2eeb5270200af8b59e4374e1afc9fd9447a73f