There is a lot of almost dead screen/display related code in the WS. This code is left over from our attempt to move screen management into the WS. There are a few WS tests that use the code, but the tests no longer really represent reality.

The code that can be deleted once the tests are fixed:
- ScreenManagerOzoneInternal
- ScreenManagerStubInternal
- TestScreenManager
- ScreenManagerDelegate
- mojom::DisplayController
- mojom::TestDisplayController

The ScreenManager interface and the ws::DisplayManager class can be cleaned up as well when this happens.