This reverts commit 46628795.

Reason for revert: Compat breakage

Bug: chromium:1170196

Original change's description:
> Ship the relative indexing method `.at`
>
> I2S with LGTMs:
> https://groups.google.com/a/chromium.org/g/blink-dev/c/I8S78w7aFmE/m/qLHAcjhRCQAJ
>
> v8: 10961
> Change-Id: If0440c0595823c61352f144c1fc29c54a1175623
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2574716
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Shu-yu Guo <syg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71619}

TBR=marja@chromium.org,syg@chromium.org

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

Change-Id: I2384af84100dcf8cb27f10c5d055d7f864ebcbb9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2646139Reviewed-by: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72279}