This reverts commit db129b65.

Reason for revert: blocks roll: https://chromium-review.googlesource.com/c/chromium/src/+/873150

Original change's description:
> [turbofan] Speculate on bounds checks for String#charAt and String#charCodeAt.
> 
> With the new builtin optimization guard we can just speculatively assume
> that the index passed to String#charAt and String#charCodeAt (in optimized
> code) is going to be within the valid range for the receiver. This is
> what Crankshaft used to do, and it avoids Smi checks on the result for
> String#charCodeAt, since it can no longer return NaN.
> 
> This gives rise to further optimizations of these builtins (i.e. to
> completely avoid the tagging of char codes), and by itself already
> improves the regression test originally reported from 650ms to
> 610ms.
> 
> Bug: v8:7127, v8:7326
> Change-Id: Ia25a555c5c1a48d229c094b1ecd2487eec81e390
> Reviewed-on: https://chromium-review.googlesource.com/872850
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50667}

TBR=yangguo@chromium.org,bmeurer@chromium.org

Change-Id: I6d393a0797cac2fdfd67487a26ac1b178bd52813
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7127, v8:7326
Reviewed-on: https://chromium-review.googlesource.com/873355Reviewed-by: Michael Hablich (vacation) <hablich@chromium.org>
Commit-Queue: Michael Hablich (vacation) <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50672}