Revert of [regexp] implement /ui to mirror the implementation for /i.

test/mjsunit/harmony/unicode-regexp-ignore-case.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --harmony-unicode-regexps
 
 // Non-unicode use toUpperCase mappings.
 assertFalse(/[\u00e5]/i.test("\u212b"));
 assertFalse(/[\u212b]/i.test("\u00e5\u1234"));
 assertFalse(/[\u212b]/i.test("\u00e5"));
@@ skipping 38 matching lines @@
 
 // Back references.
 assertEquals(["\u00e5\u212b\u00c5", "\u00e5"],
              /(.)\1\1/ui.exec("\u00e5\u212b\u00c5"));
 assertEquals(["\u{118aa}\u{118ca}", "\u{118aa}"],
              /(.)\1/ui.exec("\u{118aa}\u{118ca}"));
 
 // Misc.
 assertTrue(/\u00e5\u00e5\u00e5/ui.test("\u212b\u00e5\u00c5"));
 assertTrue(/AB\u{10400}/ui.test("ab\u{10428}"));
+
+// Non-Latin1 maps to Latin1.
+assertEquals(["s"], /^\u017F/ui.exec("s"));
+assertEquals(["s"], /^\u017F/ui.exec("s\u1234"));
+assertEquals(["as"], /^a[\u017F]/ui.exec("as"));
+assertEquals(["as"], /^a[\u017F]/ui.exec("as\u1234"));