1. Toss the game into a campfire.
Pros: The save data is gone. Like, way, way gone.
Cons: Liquified cartridges are notoriously hard to insert back into systems.
2. Purchase the NDS Adaptor Plus, a doodad that can be used to back up save data to PC, and to eradicate save games.
Pros: The game can still be played.
Cons: Campfires are free, and the NDS Adapter Plus will cost you some money.
We'll let you ruminate on this one for a bit.