[Status Bar Refactor] 3/3: Remove HeadsUpAppearanceController#destroy and

migrate the controller to a ViewController model instead.

This allows us to not have to keep track of old HUACs anymore!

Test: atest SystemUITests
Test: manual (verified via logging that #onDetach is called at the same
points that #destroy would have been called)
Bug: 205609837

Change-Id: I32b5df3306616a75ffe009c81b8966689fd11dda