Revert of [builtins] Migrate String.prototype.charCodeAt and String.prototype.charAt to TurboFan. (patchset #2 id:20001 of https://codereview.chromium.org/1868963002/ )

Reason for revert:
Needed to revert https://codereview.chromium.org/1838283003/

Original issue's description:
> [builtins] Migrate String.prototype.charCodeAt and String.prototype.charAt to TurboFan.
>
> Make these builtins fast by default w/o relying on the
> %_StringCharCodeAt and %_StringCharAt intrinsics, which we cannot deal
> with well in TurboFan (and ignition).
>
> R=epertoso@chromium.org
>
> Committed: https://crrev.com/43d3331d87f68ea7efa1b58f559f33f60e5dacfb
> Cr-Commit-Position: refs/heads/master@{#35350}

TBR=epertoso@chromium.org,bmeurer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1870993002

Cr-Commit-Position: refs/heads/master@{#35351}