This reverts commit 54379af9.

Reason for revert: Big performance regressions, need to investigate

Original change's description:
> [wasm] Remove fixed limit on number of background tasks
> 
> After fixing https://crbug.com/v8/8916, background compilation scales
> far beyond 10 threads, especially for TurboFan (where much more work is
> parallelizable). Thus, remove the limit of 10 background compilation
> tasks, and use all available threads instead.
> 
> R=​mstarzinger@chromium.org
> 
> Bug: v8:8916
> Change-Id: I13c30777e3c85b2de7901b5eac3e6a41457a56f9
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1893348
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64724}

TBR=mstarzinger@chromium.org,clemensb@chromium.org

Change-Id: I180cff9f39d8960aa793f279cfb61b7444992bc6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8916
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1897889Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64748}