Stub out BackgroundApp/FastOverview states for Go.

Go's recents will not have swipe up to overview so there is no need to
have BackgroundAppState. We also do not support quickstep so we don't
need a distinct FastOverviewState. So we stub them out here.

Bug: 114136250
Test: Manual test Launcher3QuickstepGo + NexusLauncher
Change-Id: I9223cd35fc3c64688cda16dcaa1d5f40460c9323