Remove exception whe Colorized notificiation uses COLOR_DEFAULT.

This restores behavior of API 30 that ensures that ranking is unaffected by the notification's color.  Specifically, this allows apps to set COLOR_DEFAULT on Colorized notifications, which in future versions may result in using a system-provided (theme-dependant) background color.

Bug: 187508265
Test: atest NotificationComparatorTest NotificationTest AppOpsCoordinatorTest NotificationGutsManagerTest NotificationManagerServiceTest NotificationBuilderTest
Change-Id: I4a61e9c8dc75871b79ec5ed5ce4416343e8d014f