This reverts commit 273f4e42.

Reason for revert: Based on another need that needs to be reverted because of TSAN failures.

Original change's description:
> [heap] Avoid ParkedMutexGuard during allocation
> 
> Since main thread allocation does not start incremental marking anymore
> while holding allocation_mutex_, background allocation does not need
> ParkedMutexGuard anymore to avoid deadlocks.
> 
> This also means background thread allocation isn't paused anymore to
> perform a GC, which already resulted in subtle bugs (e.g. in
> ExpandBackground with incremental marking). We also do not
> stop-the-world anymore while holding allocation_mutex_.
> 
> Bug: v8:10315
> Change-Id: Iadf00bc26434c765722b82a10497ab06151f15cc
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2289771
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#68754}

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

Change-Id: I3a16c13626c891e8063564fc05fd2d3fc427d159
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10315
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2289975Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68761}