Fix 404

Originally we had a stamp block that we were going to use in frozen. We didn't end up using it anywhere, but I want to leave it in the code as it's something we'll probably want elsewhere in the future.

snowflake.png existed in the elsa skin, but not in the anna skin, resulting in a 404 in anna levels

Fix removes the image from both skins (since unused) and also from the turtle_stamp block.