[CS] Remove unused methods from CentralSurfaces interface.

`start` and `dump` can be removed because they're covered by
`CentralSurfacesImpl` implementing `CoreStartable`.

Bug: 277764509
Test: `adb shell dumpsys activity service
com.android.systemui/.SystemUIService CentralSurfacesGoogle` -> dumps
CentralSurfaces info
Test: atest CentralSurfacesImplTest

Change-Id: Ie546c1896051e94379603837f4aca75233075b50