This reverts commit 2c0b1f6e.

Reason for revert: Seems to cause GC stress failures blocking LKGR:
https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20gc%20stress/22453
https://ci.chromium.org/p/v8/builders/ci/V8%20Mac64%20GC%20Stress/7318

Original change's description:
> [turbofan] re-wire Unreachable to the graph end at EffectPhi's
> 
> This avoids the EffectControlLinearizer stumbling upon unreachable
> code.
> 
> Bug: chromium:958718
> Change-Id: I135c17813741e48e878a4624370eee1e06081031
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1605737
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61434}

TBR=jarin@chromium.org,tebbi@chromium.org

Change-Id: I85cf33f06617b15cdd435e2699ace99e532d26e2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:958718
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1607655Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61436}