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

Bug: v8:10713
Change-Id: I5d02e946f3bf9fe08f943a811f2d3cc8aec81ea8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2486233Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70635}