This reverts commit c7aef552.

Reason for revert: Merged the wrong CL for the fix.

Original change's description:
> [maglev] Fix dead fallthrough merging
>
> Add a method which optionally merges dead fallthrough paths, in case the
> iteration in EmitUnconditionalDeopt reaches a merge point that is live
> from another jump but dead on the fallthrough.
>
> Bug: v8:7700
> Change-Id: Ie505cd5356fcf70208f2f6d3e52b805956485f74
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3663086
> Auto-Submit: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Toon Verwaest <verwaest@chromium.org>
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#80878}

Bug: v8:7700
Change-Id: I75a21777aecfa08138fcc25a882ae109f3409159
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3687649
Auto-Submit: Leszek Swirski <leszeks@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/main@{#80917}