Remove --experimental-classes flag and related dead code.

src/ast-this-access-visitor.h

-// Copyright 2014 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.
-
-#ifndef V8_AST_THIS_ACCESS_VISITOR_H_
-#define V8_AST_THIS_ACCESS_VISITOR_H_
-#include "src/ast.h"
-
-namespace v8 {
-namespace internal {
-
-class AstThisAccessVisitor : public AstVisitor {
- public:
-  AstThisAccessVisitor(Isolate* isolate, Zone* zone);
-
-  bool UsesThis() { return uses_this_; }
-
-#define DECLARE_VISIT(type) void Visit##type(type* node) OVERRIDE;
-  AST_NODE_LIST(DECLARE_VISIT)
-#undef DECLARE_VISIT
-
- private:
-  bool uses_this_;
-
-  void VisitIfNotNull(AstNode* node) {
-    if (node != NULL) Visit(node);
-  }
-
-  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
-  DISALLOW_COPY_AND_ASSIGN(AstThisAccessVisitor);
-};
-}
-}  // namespace v8::internal
-#endif  // V8_AST_THIS_ACCESS_VISITOR_H_