Basically, `BeatmapCarousel.CurrentSelection`, which is
magic-object-typed, can no longer use `BeatmapInfo` directly, it now
must also use `GroupedBeatmap`.
This spills out all the way into song select because of beatmap
selection flows that require hookup from song select.
Test was added in 5495c2090a to exercise a
previous version of the hotfix-workaround of not allowing seeking back.
Now that the hotfix-workaround also encompasses seeking *forward*, which
breaks another 100 tests, thus requiring the hotfix-workaround to be
turned off for tests, this situation is just completely out of
control. So I'm just removing the test because ugh.