This reverts commit 3e1c7040.

Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20concurrent%20marking/12665

Original change's description:
> Reland "cppgc: Add page memory allocation backend"
> 
> This is a port of src/components/gc that was added recently.
> 
> Differences:
> - Added back bucketing to the page pool, as that guarantees that
>   arenas used for specific types do not have their pages used by other
>   arenas.
> - Replaced base::flat_map with std::map. This may cause performance
>   regressions when using PageMemoryRegionTree in hot paths. A
>   vector-like representation may be used to fix such a regression
> 
> This reverts commit 656c68a7.
> 
> Bug: chromium:1056170
> Change-Id: I638183c944255ebcaab47d2b94b1980d54479746
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2143814
> Reviewed-by: Maya Lekova <mslekova@chromium.org>
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67080}

TBR=mlippautz@chromium.org,mslekova@chromium.org

Change-Id: I04b048dd979c32e9275c972307796d5f75865037
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144114Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67084}