Knuckles whirlwind jump into shield switch causes landing in land frames

Happens because Whirlwind removes his jump flags, and being thokked in fall frames counts as the landing conditions.

Two ideas to fix this:

1. Just make the whirlwind jump apply PF_NOJUMPDAMAGE instead of removing jump flags entirely.
2. Change the conditions for the landing to apply so it's more difficult to trigger accidentally.

mentioned in merge request !1740 (merged)

added Bug label

closed with merge request !1740 (merged)

mentioned in commit 50bdc5f1

mentioned in commit 6604f479