This reverts commit dcd91455.

Reason for revert: Breaks TSAN no-concurrent-marking - https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20no-concurrent-marking/3341/overview

Original change's description:
> [heap] Do not scan main thread handles when starting marking
>
> We do not need to scan main thread handles when starting incremental
> marking. This reduces the time to start incremental marking.
>
> Bug: v8:11645
> Change-Id: Ib99a13e7875f50fbfe5346ac0e186d8960ea1337
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2826124
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#73994}

Bug: v8:11645
Change-Id: I5e2325ef326b79b1807b52384cc5473d126ca6cb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2831482
Auto-Submit: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#73997}