Orbit: remove `.animate-in` late (just before setting `.active`)

This fixes the animations, especially with `variable_height` handling,
where the slide content would slide in, but then disappear until the
final animation of the containers height gets done / is finished.
Merge pull request #4909 from blueyed/orbit-remove-animate-in-late

Orbit: remove `.animate-in` late (just before setting `.active`)