This reverts commit 361bb1a0.

Reason for revert: See https://crbug.com/v8/6981

BUG=v8:6981

Original change's description:
> [test] Refactor assertPromiseResult
>
> This patch introduces assertPromiseFulfills and assertPromiseFulfills as
> a replacement for assertPromiseResult because it’s more JavaScript-y.
>
> BUG=v8:6921
> R=ahaas@chromium.org
>
> Also-By: ahaas@chromium.org
> Change-Id: I2f865dba3992ddf3b58987bf0b376d143edb5c31
> Reviewed-on: https://chromium-review.googlesource.com/718746
> Commit-Queue: Andreas Haas <ahaas@chromium.org>
> Reviewed-by: Andreas Haas <ahaas@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48578}

Change-Id: Ie760d2422451f16acc616aae001fe9fd18bf5cd4
Reviewed-on: https://chromium-review.googlesource.com/738249Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48936}