Redesign Stealth Checkpoint Placement

[PlayMatters]

Following todays playtest, I'll redesign the Checkpoints for the Stealth level for better playability and less tileset blockers.

[wjt]

As discussed on #603, given that the KnitWitch asset is floating, I think we can just remove the collision shape from the checkpoints when we integrate that, and have the player pass through the KnitWitch (it's some kind of spectral entity without a true corporeal form???).

[wjt]

@PlayMatters try https://endlessm.github.io/threadbare/#quests/lore_quests/quest_001/3_stealth_level/stealth_level now – I have added the KnitWitch and removed its collision shape so the player can walk through it. See what you think.

[manuq]

What is the status of this, @PlayMatters ?