Drive-by: clean up SubS64/AddS64 macroassembler
Change-Id: I31a15b1f3f3825122f6857861845c8961ece3649
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3024152
Commit-Queue: Junliang Yan <junyan@redhat.com>
Reviewed-by: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#75711}