ReduceArrayIndexOfIncludes didn't account for kUnreliableReceiverMaps.
Will think about a more robust mechanism for this.

Bug: chromium:944062
Change-Id: Ib2bdaf4399225de4413e12c5684f58dfe524a2cd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1532331
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60400}