Revert of Ship --harmony-regexp-exec (patchset #3 id:40001 of https://codereview.chromium.org/1847103002/ )

Reason for revert:
breaks some chromium browser_tests: https://codereview.chromium.org/1848233002/

Original issue's description:
> Ship --harmony-regexp-exec
>
> There are still spec compliance fixes to be made, but this patch
> turns the flag to shipping to make sure we get more canary coverage
> and performance data from the bots.
>
> BUG=v8:4602
> LOG=y
>
> Committed: https://crrev.com/84492bb66b340f4e0df36758e98fddbb10b5d1dc
> Cr-Commit-Position: refs/heads/master@{#35181}

TBR=littledan@chromium.org,adamk@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4602

Review URL: https://codereview.chromium.org/1852673003

Cr-Commit-Position: refs/heads/master@{#35198}