This reverts commit b7db5cd9
(https://codereview.chromium.org/1324353002/).

Our internal dashboard shows that this patch has introduced massive (3x) performance regressions for string ops. This is probably due to it repeatedly invoking %_StringCharCodeAt in a loop, which is far from cheap (has to dispatch on one of our 30+ string representations each time).

TBR=dehrenberg@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1439083003

Cr-Commit-Position: refs/heads/master@{#31981}