Revert "The set b, which temporarily stores ChunkPositions, will be a threadLocal variable to avoid concurrent modification of it, when multiple thread use it. The previous approach in commit 923dc58197 had worked too, but required the accessing threads to wait for each other, because of the lock they were taking."

This reverts commit 0870b0ba975161b8761207f2dee27ad372e97cb0.
Revert "This reverts commit 923dc58197"

This reverts commit 3dfc54c7af492d4e3408d97a7d93f2c7f4191386, and
reapplies the synchronization of the HashSet b in BlockRedstoneWire