This reverts commit d4056c61.

Reason for revert: Fails on GCC, please check https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20gcc/6184

Original change's description:
> 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
> 
> Bug: chromium:1056170
> Change-Id: I03e3abe55faf7bb50c8011dafc23396889bf66db
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2139586
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67073}

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

Change-Id: I1e421898bb8a08f32d8eb2355ed547e0ee38b429
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2140949Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67074}