Remove now defunct MessageBuilder class.

mojo/mojo.gyp

 # Copyright 2013 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.
 
 {
   'variables': {
     'chromium_code': 1,  # Use higher warning level.
   },
   'target_defaults': {
     'defines': ['MOJO_IMPLEMENTATION'],
   },
   'targets': [
     {
       'target_name': 'mojo',
       'type': 'none',
-      'dependencies': [
-        'mojo_message',
-      ],
-    },
-    {
-      'target_name': 'mojo_message',
-      'type': 'static_library',
-      'include_dirs': [
-        '..',
-      ],
-      'sources': [
-        'public/libs/message/message.cc',
-        'public/libs/message/message.h',
-        'public/libs/message/message_builder.cc',
-        'public/libs/message/message_builder.h',
-      ],
-    },
-    {
-      'target_name': 'mojo_unittests',
-      'type': 'executable',
-      'dependencies': [
-        'mojo_message',
-        '../base/base.gyp:run_all_unittests',
-        '../testing/gtest.gyp:gtest',
-      ],
-      'include_dirs': [
-        '..'
-      ],
-      'sources': [
-        'public/libs/message/message_unittest.cc',
-      ],
     },
   ],
 }