This project has moved to Planet Minecraft.
This data pack kills any Wither Boss not spawned in a Nether Fortress, and drops the 4 soulsand and 3 wither skulls (so they aren't wasted). This will prevent users from using the bedrock under the End Portal, or in the Nether roof, to trap the Wither in order to avoid the danger of fighting it in an open space. The only valid place to spawn a Wither is a Nether Fortress, so the boss fight should be dangerous again.
More information about data packs and how to use them can be found on the official Minecraft Wiki.