Remove deprecated TracedGlobal<>, greatly simplifying handling of
traced references in general.

Also saves a word per v8::TracedReference as there's no need to keep a
possible callback around.

Bug: v8:12603
Change-Id: Ice35d7906775b912d02e97a27a722b3e1cec28d9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3532251Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79589}