This reverts commit 34625fdb.

Reason for revert: Test caused timeout, investigating.

Original change's description:
> [Builtins] Array.prototype.forEach perf regression on dictionaries.
> 
> An unnecessary call to ToString() on the array index caused trips to
> the runtime. The fix also includes performance micro-benchmarks so
> we'll have a harder time regressing this case in future.
> 
> Bug: v8:8112
> Change-Id: Iada5bd2e3c6d2246fb1225e7094f3d9c66ddafbd
> Reviewed-on: https://chromium-review.googlesource.com/1206355
> Commit-Queue: Michael Stanton <mvstanton@chromium.org>
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55653}

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

Change-Id: I21de9b9b33edf03f2173f579c4ba0fc3dfd8ff88
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8112
Reviewed-on: https://chromium-review.googlesource.com/1209288Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55681}