Refine the DarkModeScheduleSelectorController

- move the initial part to the displayPreference.
- use indext compared instead of the direct string compared.

Bug: 141567787
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=ROBOTEST_FILTER=com.android.settings.display
Change-Id: I49ccc248bc1f5f9659f8543793ea502ac3e2ea6f
3 files changed