Remove utilities that are unused, as well as replacing
the full chunk map with a concurrentutil implementation.
Additionally, fix the addition/removal of chunks to/from the
full chunk map so that getChunkIfLoaded correctly returns a
non-null chunk when calling the load or unload events.
When ChunkAccess was converted to an abstract class some versions
ago, the code to initialise nibble arrays should have been moved.
However, the code was not moved and so now mods constructing their
own implementations of ChunkAccess would not have the nibble arrays
initialised.
This is ported to Paper from Starlight to keep the code base in sync,
not because it fixes anything known.
When per-player mob spawning is enabled we do not need to randomly
shuffle the chunk list. Additionally, we can use the NearbyPlayers
class to quickly retrieve nearby players instead of possible
searching all players on the server.
