This reverts commit e2aa734a.

Reason for revert:  speculative revert for https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Mac64%20-%20debug/31901/blamelist

Original change's description:
> [wasm-simd][arm] Prototype i8x16.popcnt
>
> Bug: v8:11002
> Change-Id: Ib97e51ed52249a1af7a4b879396b70a016991719
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2567534
> Commit-Queue: Zhi An Ng <zhin@chromium.org>
> Reviewed-by: Bill Budge <bbudge@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71552}

TBR=bbudge@chromium.org,jkummerow@chromium.org,v8-arm-ports@googlegroups.com,zhin@chromium.org

Change-Id: Id1ae2dbaae52d45eb81ba8636178236ca8e9f7e0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:11002
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2568925Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71554}