This reverts commit 2afb00c0.

Reason for revert: Some tests started to timeout.

Original change's description:
> [heap] Remove SWEEPING phase in incremental marking
>
> The SWEEPING phase in incremental marking was used to finish sweeping
> of the last GC cycle concurrently before starting incremental marking.
> This avoids potentially long pauses when starting incremental marking.
> However this shouldn't be necessary in most cases where sweeping is
> already finished when starting the next cycle. The implementation also
> didn't cleanly separate the GC cycles.
>
> In case the sweeping phase is necessary for pause times, we can
> introduce a "CompleteSweep" phase which runs right before starting
> incremental marking.
>
> Change-Id: Iaff8c06d5691e584894f57941f181d0424051eec
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2567707
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71555}

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

Change-Id: I9adea60c21ff7cdfa7bbac3e6a4a240640fa5ea9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2569766Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71570}