This reverts commit 5ef4e14f.

Reason for revert: Seems to be causing a lot of flakes
e.g., https://ci.chromium.org/p/v8/builders/ci/V8%20Linux64/42913

Original change's description:
> [heap] Replace usages of CollectionRequested with SafepointRequested
>
> CollectionRequested was used exclusively on the main thread when a
> background thread requested a GC. The main thread never used
> SafepointRequested at any time. Now with the shared GC we might need to
> stop multiple isolates in a safepoint in the future. In such a situation
> we would need to use SafepointRequested also on the main thread.
>
> This CL prepares V8 for this situation by using SafepointRequested
> instead of CollectionRequested and friends on the main thread. The slow
> path of Safepoint(), Park() and Unpark() will check in the future
> whether the main thread needs to halt for a shared GC or needs to
> perform a local GC. At the moment, simply performing the local GC is
> still enough.
>
> Bug: v8:11708
> Change-Id: I819b6f7db8251074a4adf8b554e0a1393c76f7da
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2891834
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#74673}

Bug: v8:11708
Change-Id: I51c51e68110e83f729bd43ef62eef1396aa0cb96
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2906913
Auto-Submit: Francis McCabe <fgm@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@{#74684}