Forge/MCPC+: disable Forgotten Nature world gen for now, conflicts with Dimensional Doors

Temporarily disabled to fix hang when entering Dimensional Door.
Existing generation preserved, and can re-enable when needed.
Hang: https://gist.github.com/agaricusb/5376959
Confirmed at http://www.minecraftforum.net/topic/1519278-forgotten-nature-mc151v129major-addition-to-nature-in-mc-trees-crops-fruit-flowers-biomes-fences-stone/page__st__760#entry22474962