Revert "The set b, which temporarily stores ChunkPositions, will be a threadLocal variable to avoid concurrent modification of it, when multiple threads use it. The previous approach in commit 33c1534bdf had worked too, but required the accessing thread to wait for each other, because of the lock they were taking."

This reverts commit ce646ec9202fe226b16e70f5655a855932842133.
Revert "This reverts commit 33c1534bdf"

This reverts commit 4084dd41d70495cf62b377ec5f908e1a1f66a9e0, and
reapplies the synchronization of the HashSet b in BlockRedstoneWire