This reverts commit 5ea58bde.

Reason for revert: potential perf regression.

BUG=chromium:748100

Original change's description:
> [heap] Use AdjustAmountOfExternalMemory to account freed array buffers.
> 
> Currently GC decrements the external memory counter directly bypassing
> the AdjustAmountOfExternalMemory. This is inconsistent with array
> buffer allocation, which actually uses the API to increment the counter.
> 
> Change-Id: I401087872213fdd60f1a40c99c8f459c14dc0608
> Reviewed-on: https://chromium-review.googlesource.com/582008
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46835}

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

Change-Id: Ibde2acb9ae2e4274946124fc4606321b95c80758
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/583453Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46847}