Merge NSSL and CLOCK migration flags

It will be easier to progress these as a unit.

Fixes: 325271165
Test: atest SystemUITests
Flag: ACONFIG com.android.systemui.migrate_clocks_to_blueprint
DEVELOPMENT
Flag: ACONFIG com.android.systemui.keyguard_bottom_area_refactor
STAGING

Change-Id: I084b838d17d7e7330421864e1ed2d47ec92a8c23