Remove the Quallenalarm (jellyfish) typing minigame

Letters-round lessons only had bubbles and jellyfish as eligible arcade
modes; with jellyfish gone, bubbles is now always used instead of the
two alternating - no lessons need to be dropped.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

python-backend/tests/test_tippen_curriculum.py

@@ -244,11 +244,10 @@ def test_plays_a_mode_that_fits_its_kind(curriculum) -> None:
             assert mode in ELIGIBLE_MODES[lesson.kind], where
 
 
-def test_never_plays_the_same_arcade_game_twice_in_a_row(curriculum) -> None:
-    arcade = [lesson for lesson in curriculum.lessons if lesson.kind == "letters"]
-    for i in range(1, len(arcade)):
-        where = f"{arcade[i].number}: {arcade[i].title}"
-        assert arcade[i].primary_mode != arcade[i - 1].primary_mode, where
+def test_letters_rounds_always_play_bubbles(curriculum) -> None:
+    for lesson in curriculum.lessons:
+        if lesson.kind == "letters":
+            assert lesson.primary_mode == "bubbles", f"{lesson.number}: {lesson.title}"
 
 
 def test_offers_every_eligible_mode_not_gated_on_as_a_bonus(curriculum) -> None: