This reverts commit 0938188f.

Reason for revert: new test times out on tsan: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN/35152/overview

Original change's description:
> [wasm][debug] Garbage-collect stepping code
>
> All wasm code has an initial ref count of 1, in the expectation that it
> will be added to the code table. When the code is removed from that
> table, the ref count will be decremented.
> Stepping code (and also other code under special circumstances) will not
> be added to the code table though. Hence the ref count will never be
> decremented below 1, and the code will never be garbage-collected.
>
> This CL fixes this, by decrementing the ref count if the code is not
> added to the code table.
> Note that the code will only be collected if no isolate is currently
> using it, so it won't be collected while still in use for stepping.
>
> R=​thibaudm@chromium.org
>
> Bug: chromium:1168564
> Change-Id: I3047753591cbc52689ca019e9548ec58c237b835
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2649040
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#72354}

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

Change-Id: I84f84324d2c4a3cae2ae6b97f469e3f22b0e3b3f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1168564
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2652485Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72357}