CraftBukkit removed their implementation that caused this issue,
switching to Mojang's implementation which doesn't appear to share it. I
already removed the important bit in the last upstream merge, this is
just unused and unnecessary now. So we remove it.
getting a loaded chunk is one of the most hottest pieces of code in the game.
Often, getChunkAt is called for the same chunk multiple times in a row, often
from getType();
Optimize this look up by using a Last Access cache.
