The function is no longer used in Chromium or V8 and can therefore be
deleted. This CL also simplifies V8::GetSandboxSizeInBytes, which now no
longer needs to be able to deal with an uninitialized sandbox.

Bug: v8:10391
Change-Id: I22d6b0e03de1fd2ba3d38c4e476fca44068b62f9
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/+/3769690Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82583}