Revert "Makes the LinkedTransferQueue in the embedded ForkJoin library use s.c.u.Updaters"

This reverts commit bd8f41c9add384505e13831ad150c0cd8d9ff113.
Revert "Makes Promise use s.c.u.Updaters instead of s.m.Unsafe"

This reverts commit f3431f6130e202e4660527fe006b7ef1bc7c09ab.
Revert "Adds relaxedGet and relaxedSet to Updaters.UnsafeX"

This reverts commit ca01ddeec134a71cc1ef6d57be27245a6bb4f40c.
Revert "Adds scala.concurrent.util.Updaters"

This reverts commit 788c3799330d7ab93aed0baef9da0873df4940df.
Removes the AtomicReferenceFieldUpdater for AbstractPromise—it is unused