This reverts commit 76195d9e.

Reason for revert: New parallel tests timeout on the waterfall (I think because it's configured to use less worker threads and TaskProcessingOneItem is currently designed to steal a worker but only process one item...).

Original change's description:
> Smoother distribution of worker assignment in parallel task array.
> 
> This is a merge of https://chromium-review.googlesource.com/c/v8/v8/+/888704
> and https://chromium-review.googlesource.com/c/v8/v8/+/887084
> 
> Which implements the fix in CL 887084 correctly in a world where
> there can be more tasks_ than items_ (crbug.com/806237).
> 
> Bug: chromium:805932
> Change-Id: I05401be4fdce442644a8973281a9d88bd959b271
> Reviewed-on: https://chromium-review.googlesource.com/892883
> Commit-Queue: Gabriel Charette <gab@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50956}

TBR=gab@chromium.org,hpayer@chromium.org,mlippautz@chromium.org

Change-Id: Icf52eb3afeb9467557c1e0db6922d590466943f0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:805932
Reviewed-on: https://chromium-review.googlesource.com/893462Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50965}