The DCHECK on number_of_elements was making TSAN unhappy. Given that
making this field atomic would be a performance penalty, and that the
DCHECK isn't expected to catch any errors in practice (other DCHECKs
check the same invariant), we can just drop it.

Bug: v8:11183
Change-Id: Ic1b5697b233c4c45c3951816531f888459c3e69f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2567698
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71527}