We don't need to keep JSToObject operations in the graph if there's some
preceeding map check that already provides information that the input is
indeed already a receiver.

Change-Id: I2d04895831ff561624fbe91a2fe03bb6e5d918a5
Reviewed-on: https://chromium-review.googlesource.com/1174259Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55120}