V8_SANDBOX has been renamed to V8_ENABLE_SANDBOX in crrev.com/c/3647355
and its remaining uses in Chromium have now been renamed as well.

Bug: v8:10391
Change-Id: Ibb23ecab6687438b462685ef7fa044c0024dd098
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng,v8_linux_arm64_sim_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3660251Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80739}