This reverts commit 90ea9b35.

Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Mac64%20-%20debug/31274?

Original change's description:
> cppgc: Port backing store compaction.
>
> This CL ports the existing backing store compaction algorithm from
> blink. It does not attempt to improve on the existing algorithm.
>
> Currently only unified heap uses the compaction implementation. It is
> never triggered through standalone GCs.
>
> The compaction implementation resides within an internal "subtle" namespace.
>
> Bug: v8:10990
> Change-Id: I4aa781db1b711e7aafc34234c4fb142de84394d7
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2485228
> Commit-Queue: Omer Katz <omerkatz@chromium.org>
> Reviewed-by: Anton Bikineev <bikineev@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#70714}

TBR=mlippautz@chromium.org,bikineev@chromium.org,omerkatz@chromium.org

Change-Id: Iadae1ee0c6c0400f0e1a0a3805be5316a1d4b979
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10990
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2492330Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70716}