This reverts commit a402dd63.

Reason for revert: Breaks msan:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/builds/15197

Original change's description:
> [heap] Simplify array buffer tracker
> 
> Retrieve length from the buffer instead of storing in as value in the
> map.
> 
> Change-Id: Icdc87bb46c29fff779bf6e98139324662ced5bf6
> Reviewed-on: https://chromium-review.googlesource.com/518171
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#45600}

NOTRY=true
NOTREECHECKS=true
NOPRESUBMIT=true

TBR=mlippautz@chromium.org,jochen@chromium.org
No-Presubmit: true
No-Tree-Checks: true
No-Try: true

Change-Id: I22e3590528beb911d366b9d93ec302857a631971
Reviewed-on: https://chromium-review.googlesource.com/518117
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45606}