This reverts commit e83ee945.

Reason for revert: Check failure in regress-v8-6940.js

Original change's description:
> RegExp: Add the ability to switch flags on and off within the regexp.
> 
> This is a reland of https://chromium-review.googlesource.com/c/v8/v8/+/752522
> which was itself a reupload of
> https://chromium-review.googlesource.com/c/v8/v8/+/571746 where reviews took
> place.
> 
> R=​yangguo@chromium.org
> 
> Bug: 
> Change-Id: Ia4dbdd6e9a362e272753ff10dc66b7f72d81ee20
> Reviewed-on: https://chromium-review.googlesource.com/753596
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Erik Corry <erikcorry@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49129}

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

Change-Id: I5ee94c47606101d06010c9e6b4b78ca51566b60a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/754682Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49130}