ES6: Remove __proto__ setter poison pill

src/messages.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 86 matching lines @@
   invalid_weakset_value:         ["Invalid value used in weak set"],
   not_date_object:               ["this is not a Date object."],
   observe_non_object:            ["Object.", "%0", " cannot ", "%0", " non-object"],
   observe_non_function:          ["Object.", "%0", " cannot deliver to non-function"],
   observe_callback_frozen:       ["Object.observe cannot deliver to a frozen function object"],
   observe_invalid_accept:        ["Object.observe accept must be an array of strings."],
   observe_type_non_string:       ["Invalid changeRecord with non-string 'type' property"],
   observe_perform_non_string:    ["Invalid non-string changeType"],
   observe_perform_non_function:  ["Cannot perform non-function"],
   observe_notify_non_notifier:   ["notify called on non-notifier object"],
-  proto_poison_pill:             ["Generic use of __proto__ accessor not allowed"],
   not_typed_array:               ["this is not a typed array."],
   invalid_argument:              ["invalid_argument"],
   data_view_not_array_buffer:    ["First argument to DataView constructor must be an ArrayBuffer"],
   constructor_not_function:      ["Constructor ", "%0", " requires 'new'"],
   not_a_promise:                 ["%0", " is not a promise"],
   resolver_not_a_function:       ["Promise resolver ", "%0", " is not a function"],
   promise_cyclic:                ["Chaining cycle detected for promise ", "%0"],
   array_functions_on_frozen:     ["Cannot modify frozen array elements"],
   array_functions_change_sealed: ["Cannot add/remove sealed array elements"],
   // RangeError
@@ skipping 1238 matching lines @@
     %GetAndClearOverflowedStackTrace(this);
   };
 
   %DefineOrRedefineAccessorProperty(
       boilerplate, 'stack', getter, setter, DONT_ENUM);
 
   return boilerplate;
 }
 
 var kStackOverflowBoilerplate = SetUpStackOverflowBoilerplate();