[Reland] Mojo: Eliminate duplicate C API symbols

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.
 
 {
-  'includes': [
-    'mojo_variables.gypi',
-  ],
   'targets': [
     {
       # GN version: //mojo
       'target_name': 'mojo',
       'type': 'none',
       'dependencies': [
         'mojo_base.gyp:mojo_base',
         'mojo_edk_tests.gyp:mojo_edk_tests',
         'mojo_public.gyp:mojo_public',
       ],
     },
   ]
 }