This reverts commit 5c59ba4f.

Reason for revert: requires more thinking 

Original change's description:
> [ic] Fix KeyedLoadIC for ArrayIndex access
> 
> Previously, without support for converting strings to numbers we'd
> switch to megamorphic state and go to the runtime always to do the
> conversion causing a performance cliff.
> 
> This patch improves the following js-perf-test scores:
> Object-Lookup-String-Constant-BytecodeHandler: 4.25%
> Object-Lookup-Index-String-BytecodeHandler: 5.41%
> 
> Bug: v8:9449
> Change-Id: I63787fa84373fc946f1304b0141e48a52a1b4bcb
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1690953
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63293}

TBR=mythria@chromium.org,jyan@ca.ibm.com,gsathya@chromium.org,leszeks@chromium.org,ishell@chromium.org,verwaest@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:9449
Change-Id: I6b6ad5901175c2e6bbd7516b13e91471adb5776d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1765532Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63347}