This reverts commit 80caf2cf.

Reason for revert: Breaks gpu tests:
https://ci.chromium.org/p/v8/builders/ci/Win%20V8%20FYI%20Release%20(NVIDIA)/5570
# Debug check failed: !possibly_empty_buckets->Contains(bucket_index).

Original change's description:
> [heap] Reduce size of possibly empty buckets
> 
> Before this CL a byte was used per bucket to store whether the bucket
> is possibly empty or not. This CL changes this such that each bucket
> only needs a single bit.
> 
> PossiblyEmptyBuckets is now a word in the page header. If more bits
> are needed than fit into a single word, an external bitmap is
> allocated using AlignedAlloc. Storing this on the page header, allows
> to remove initial_buckets from the SlotSet. The SlotSet allocation is
> then again a power-of-2 in release mode.
> 
> Change-Id: If61fd5cfa153f98757beeb444a530f6e2803fdb6
> Bug: chromium:1023139
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1906376
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64991}

TBR=ulan@chromium.org,dinfuehr@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:1023139
Change-Id: Ia90b07b9562af934dacba012da31e4f172f2922d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1918258Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65001}