This reverts commit 8e9eba36.

Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20noi18n%20-%20debug/builds/18887

Original change's description:
> [regexp] fix Latin1 ignore-case bug.
> 
> R=​jgruber@chromium.org
> 
> Bug: v8:6703
> Change-Id: I6b251191cc00d9ac8db41b91b528c130d1b23fc6
> Reviewed-on: https://chromium-review.googlesource.com/897523
> Commit-Queue: Yang Guo <yangguo@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51088}

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

Change-Id: I09138cedb2631640709ec717045247362f653cb2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6703
Reviewed-on: https://chromium-review.googlesource.com/901184Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51090}