Clean up legacy "optimization mode" design.

We have two different "Optimization mode" page design in the android R to support bi-state for AOSP and tri-state for Pixel device. From android T, we always show tri-state for both AOSP and Pixel. So it's time to clean up the legacy design for bi-state.
This change doesn't include string resources cleanup, which will be
included in a separated cl.

Bug: 232037602
Test: make RunSettingsRoboTests
Change-Id: I5194201d0b11e2dcea958d49bf07ed837a386465