Revert of [regexp] restrict pattern syntax for unicode mode. (patchset #6 id:120001 of https://codereview.chromium.org/1645573002/ )

Reason for revert:
[Sheriff] Breaks layout tests:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/4222

Original issue's description:
> [regexp] restrict pattern syntax for unicode mode.
>
> ES2015 Annex B.1.4 specifies a restricted pattern language for unicode
> mode. This change reflects that, based on some test262 test cases.
>
> R=littledan@chromium.org
> BUG=v8:2952
> LOG=N
>
> Committed: https://crrev.com/e918c4ec464456a374098049ca22eac2107f6223
> Cr-Commit-Position: refs/heads/master@{#33584}

TBR=vogelheim@chromium.org,yangguo@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:2952

Review URL: https://codereview.chromium.org/1648673002

Cr-Commit-Position: refs/heads/master@{#33588}