Both NewSpace and NewLargeObjectSpace aren't used with
FLAG_single_generation enabled. So far both spaces still existed but
weren't used in this mode. This CL makes both spaces optional, which
ensure that we do not inadvertently create objects in them or use them
in any other way.

Bug: v8:11644
Change-Id: I52a449c62e9d3df126c95419433d2abbd75539a5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2862768
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74345}