[ORC] Simplify WaitingOnGraph::Coalescer::remove. (#183175)
WaitingOnGraph::Coalescer::remove used to apply a should-remove
predicate to all SuperNodes currently registered with the coalescer.
This commit updates it to take a single SuperNode at a time, similar to
standard container erase methods.
To enable this, WaitingOnGraph::Coalescer now holds a map of registered
SuperNodes to hashes.
This allows us to remove individual SuperNodes, rather than checking all
SuperNodes in the Coalescer against a should-remove predicate.