Now that double unboxing is removed, the concurrent marker can directly
visit all JSObjects without snapshotting them first.

Bug: v8:11422
Change-Id: Ib5cb4d0b39fd2654f4e417a09c9497d134fea1ff
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2732009
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73211}