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

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
 import("//build/module_args/v8.gni")
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
@@ skipping 443 matching lines @@
     "src/api-natives.cc",
     "src/api-natives.h",
     "src/arguments.cc",
     "src/arguments.h",
     "src/assembler.cc",
     "src/assembler.h",
     "src/assert-scope.h",
     "src/assert-scope.cc",
     "src/ast-numbering.cc",
     "src/ast-numbering.h",
-    "src/ast-this-access-visitor.cc",
-    "src/ast-this-access-visitor.h",
     "src/ast-value-factory.cc",
     "src/ast-value-factory.h",
     "src/ast.cc",
     "src/ast.h",
     "src/background-parsing-task.cc",
     "src/background-parsing-task.h",
     "src/bailout-reason.cc",
     "src/bailout-reason.h",
     "src/basic-block-profiler.cc",
     "src/basic-block-profiler.h",
@@ skipping 1078 matching lines @@
       sources += [
         "src/d8-debug.cc",
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }