This CL removes registration of CppHeap as a remote tracer, and
revises LocalEmbedderHeapTracer as a switching point between CppHeap
and a remote tracer. Currently it is assumed that CppHeap and a remote
tracer are mutually exclusive and only one can be used at any given
time.

Bug: v8:12407
Change-Id: I53513d181ab63f56a88f05c3b76b47ac4dffe86f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3289167
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78132}