[strong] Remove all remainders of strong mode

test/mjsunit/strong/empty-statement.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 NoEmptySubStatement() {
-  assertThrows("'use strong'; if (1);", SyntaxError);
-  assertThrows("'use strong'; if (1) {} else;", SyntaxError);
-  assertThrows("'use strong'; while (1);", SyntaxError);
-  assertThrows("'use strong'; do; while (1);", SyntaxError);
-  assertThrows("'use strong'; for (;;);", SyntaxError);
-  assertThrows("'use strong'; for (x in []);", SyntaxError);
-  assertThrows("'use strong'; for (x of []);", SyntaxError);
-  assertThrows("'use strong'; for (let x;;);", SyntaxError);
-  assertThrows("'use strong'; for (let x in []);", SyntaxError);
-  assertThrows("'use strong'; for (let x of []);", SyntaxError);
-})();