We don't need separate Load32Zero and Load64Zero instructions, since the
implementation is LdrS and LdrD, which we already have.

Bug: v8:11038
Change-Id: I784ec8dc419c0d59de97eb2bb0b464c176dacae1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2501969
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72443}