Remove dead --use_jscre flag.

runtime/vm/regexp_test.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 
 #include "vm/isolate.h"
 #include "vm/object.h"
 #include "vm/regexp.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
-DECLARE_FLAG(bool, use_jscre);
-
 static RawArray* Match(const String& pat, const String& str) {
   Zone* zone = Thread::Current()->zone();
   const JSRegExp& regexp = JSRegExp::Handle(
       RegExpEngine::CreateJSRegExp(zone, pat, false, false));
   const intptr_t cid = str.GetClassId();
   const Function& fn = Function::Handle(regexp.function(cid));
   EXPECT(!fn.IsNull());
   const Smi& idx = Smi::Handle(Smi::New(0));
   return IRRegExpMacroAssembler::Execute(fn, str, idx, zone);
 }
@@ skipping 76 matching lines @@
   EXPECT(res_1.IsSmi());
   EXPECT(res_2.IsSmi());
 
   const Smi& smi_1 = Smi::Cast(res_1);
   const Smi& smi_2 = Smi::Cast(res_2);
   EXPECT_EQ(1, smi_1.Value());
   EXPECT_EQ(3, smi_2.Value());
 }
 
 }  // namespace dart