remove y-coord from chunks

I removed the y-coord from chunks, I hope I didn't miss anything. Fixes #1344
Now you can slaughter me for removing too much. :P
Or will travis kill this commit first? :O
That doesn't make much sense. If the chunk is not loaded now, it will be generated later on, because you're putting it to the generator's queue. The server won't send any invalid chunks to the player, it's smart enough to do so already, because even the loading is asynchronous, so the server needs to check for the chunk's existence anyway before sending to player or in fact any other activity.