Use underworld sprites for brickShrapnel

[bouveng]

When destroying bricks in underground, the sprites from underworld should be used.

[pomle]

I think this surfaces a problem with how levels is set up vs entities. With entities of different colors we explicitly say which should be there. We may want to pivot here and let levels have tiles called brick-underworld and brick-overworld instead of the color being inferred by the sprite sheet.