Remove the runtime functionality allowing the Isolate to be allocated
4GB aligned in non-pointer-compressed builds. This was barely used in
tests, so we can remove it to give slightly stronger compile-time
guarantees about pointer-compression-only methods being used only under
pointer-compression.

Change-Id: I8eb990faa8f8499ecdcb70ca104ffad4be1437b2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2442790Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70262}