[strong] Remove all remainders of strong mode

test/mjsunit/strong/use-strong.js

-// Copyright 2015 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: --strong-mode
-
-(function UseStrongScoping() {
-  assertThrows("'use strong'; 0 == 0", SyntaxError);
-  assertThrows("'use strong'; try {} catch(e) { { 0 == 0 } }", SyntaxError);
-  assertThrows("function f() { 'use strong'; 0 == 0 }", SyntaxError);
-  assertThrows("'use strong'; function f() { 0 == 0 }", SyntaxError);
-  assertThrows("'use strong'; function f() { function g() { 0 == 0 } }", SyntaxError);
-  assertTrue(eval("function f() { 'use strong' } 0 == 0"));
-  assertTrue(eval("eval('\\\'use strong\\\''); 0 == 0"));
-})();
-
-(function UseStrongMixed() {
-  assertThrows("'use strict'; 'use strong'; 0 == 0", SyntaxError);
-  assertThrows("'use strong'; 'use strict'; 0 == 0", SyntaxError);
-  assertThrows("'use strong'; 'use strong'; 0 == 0", SyntaxError);
-  assertThrows("'use strict'; function f() { 'use strong'; 0 == 0 }", SyntaxError);
-  assertThrows("'use strong'; function f() { 'use strict'; 0 == 0 }", SyntaxError);
-  assertTrue(eval("'use strict'; function f() { 'use strong' } 0 == 0"));
-  assertTrue(eval("var x; function f() { 'use strong' } delete x"));
-  assertThrows("'use strict'; var x; function f() { 'use strong' } delete x", SyntaxError);
-})();