This reverts commit 97d1ab6c.

Reason for revert: simplified lowering verifier crashes on GPU bots:
https://ci.chromium.org/ui/p/v8/builders/ci/Linux%20V8%20FYI%20Release%20(NVIDIA)/20848/overview

Original change's description:
> Reland "[turbofan] Support Phi nodes in SL Verifier"
>
> This reverts commit 82a876b0.
>
> Bug: v8:13086, v8:12619
> Change-Id: Idcc42f36b642fefb3ed706214e7385cccc89effc
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3779687
> Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
> Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82285}

Bug: v8:13086, v8:12619
Change-Id: I7a2fb19eb752403337d45de0a7ca02a5d8842766
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3820904
Auto-Submit: Adam Klein <adamk@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#82320}