This change prevents constant folding of uninhabited RefenceEqual node
because that could widen a type (from None type to the type of the
boolean constant).

Hopefully, this is a temporary workaround that will be replaced
by a better dead code elimination.

Bug: v8:6631
Change-Id: Ie25e7d710aaf1d37c9adba60f92438570843dd5d
Reviewed-on: https://chromium-review.googlesource.com/627916Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47545}