Replace OrderedMap with OrderedSet
Replace OrderedMap with OrderedSet

We weren't using notion of monoatomically increasing tick in LRU cache because
an OrderedMap does not re-order exising items that are set(), so we depend on
remove()+set(). This means the value of OrderedMap isn't used and simplifies to
OrderedSet.

adisuryadi/nuclear-js,optimizely/nuclear-js