This reverts commit 22d894c8.

Reason for revert:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Mips%20-%20builder/builds/14553

Original change's description:
> [turbofan] Add simplified operator for String.prototype.codePointAt
> 
> This CL adds the simplified operators
>   StringCodePointAt
>   SeqStringCodePointAt
> and associated lowering.
> 
> Bug: v8:7270
> Change-Id: I5aeefddeec39c3119b2d225e92a3116f802e7b45
> Reviewed-on: https://chromium-review.googlesource.com/861789
> Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50547}

TBR=sigurds@chromium.org,petermarshall@chromium.org,bmeurer@chromium.org

Change-Id: If07881fce121538cc4abc72ed5eaa42dd7829101
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7270
Reviewed-on: https://chromium-review.googlesource.com/864662Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50548}