Revert of [regexp] Port RegExpExec (patchset #2 id:20001 of https://codereview.chromium.org/2307853002/ )

Reason for revert:
Performance regressions: crbug.com/644087
Clusterfuzz: crbug.com/644074

We'll reland all regexp changes at once when the port is complete and at least performance-neutral, since the partial port requires slow workarounds.

Original issue's description:
> [regexp] Port RegExpExec
>
> BUG=v8:5339
>
> Committed: https://crrev.com/c79e163ba82f2e2dcf9b60639127d187fdbf54b9
> Cr-Commit-Position: refs/heads/master@{#39150}

TBR=bmeurer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5339

Review-Url: https://codereview.chromium.org/2315473002
Cr-Commit-Position: refs/heads/master@{#39160}