Remove all harmony runtime flags which shipped in M51

test/mjsunit/harmony/unicode-regexp-backrefs.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 --harmony-regexp-lookbehind
-
-// Back reference does not end in the middle of a surrogate pair.
-function replace(string) {
-  return string.replace(/L/g, "\ud800")
-               .replace(/l/g, "\ud801")
-               .replace(/T/g, "\udc00")
-               .replace(/\./g, "[^]");
-}
-
-function test(expectation, regexp_source, subject) {
-  if (expectation !== null) expectation = expectation.map(replace);
-  subject = replace(subject);
-  regexp_source = replace(regexp_source);
-  assertEquals(expectation, new RegExp(regexp_source, "u").exec(subject));
-}
-
-// Back reference does not end in the middle of a surrogate pair.
-test(null, "(L)\\1", "LLT");
-test(["LLTLl", "L", "l"], "(L).*\\1(.)", "LLTLl");
-test(null, "(aL).*\\1", "aLaLT");
-test(["aLaLTaLl", "aL", "l"], "(aL).*\\1(.)", "aLaLTaLl");
-
-var s = "TabcLxLTabcLxTabcLTyTabcLz";
-test([s, "TabcL", "z"], "([^x]+).*\\1(.)", s);
-
-// Back reference does not start in the middle of a surrogate pair.
-test(["TLTabTc", "T", "c"], "(T).*\\1(.)", "TLTabTc");
-
-// Lookbehinds.
-test(null, "(?<=\\1(T)x)", "LTTx");
-test(["", "b", "T"], "(?<=(.)\\2.*(T)x)", "bTaLTTx");
-test(null, "(?<=\\1.*(L)x)", "LTLx");
-test(["", "b", "L"], "(?<=(.)\\2.*(L)x)", "bLaLTLx");
-
-
-test(null, "([^x]+)x*\\1", "LxLT");
-test(null, "([^x]+)x*\\1", "TxLT");
-test(null, "([^x]+)x*\\1", "LTxL");
-test(null, "([^x]+)x*\\1", "LTxT");
-test(null, "([^x]+)x*\\1", "xLxLT");
-test(null, "([^x]+)x*\\1", "xTxLT");
-test(null, "([^x]+)x*\\1", "xLTxL");
-test(null, "([^x]+)x*\\1", "xLTxT");
-test(null, "([^x]+)x*\\1", "xxxLxxLTxx");
-test(null, "([^x]+)x*\\1", "xxxTxxLTxx");
-test(null, "([^x]+)x*\\1", "xxxLTxxLxx");
-test(null, "([^x]+)x*\\1", "xxxLTxxTxx");
-test(["LTTxxLTT", "LTT"], "([^x]+)x*\\1", "xxxLTTxxLTTxx");