The flag has been turned on for a long time and we do not intend to
support a mode without young LO objects.

A side effect is that it removes a branch in AllocateRaw for the young
generation.

Drive-by: Reinstantiate the LO space verifier checking that only
certain types can appear as large objects.

Bug: v8:12615
Change-Id: I8c33019a04670f20459ea2faa9dc2f98b8cda40b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3450420Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79044}