This reverts commit 4c7c6f73.

Reason for revert: Reverted because of TSAN failures.

Original change's description:
> [heap] Enable usage of ArrayBufferExtensions
> 
> Switch the flag to true to enable ArrayBufferExtensions by default. The
> last CL (https://crrev.com/c/2065088) that tried to enable this was
> reverted because of alignment issues on ARM64
> (fixed in https://crrev.com/c/2071256).
> 
> Bug: v8:10064
> Change-Id: I47f478c978094fb5038113eb452865748956b42e
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2074157
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#66460}

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

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

Bug: v8:10064
Change-Id: Ie15bf9858eb1f01667ea905363824cbb2bf7f884
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2078585Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66487}