Remove the usbPrivate API.

extensions/common/api/schemas.gypi

 # 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.
 
 {
   'sources': [
     '<@(schema_files)',
   ],
   'variables': {
     'chromium_code': 1,
@@ skipping 23 matching lines @@
       'sockets_tcp_server.idl',
       'sockets_udp.idl',
       'storage.json',
       'system_cpu.idl',
       'system_display.idl',
       'system_memory.idl',
       'system_network.idl',
       'system_storage.idl',
       'test.json',
       'usb.idl',
-      'usb_private.idl',
       'web_request.json',
       'web_view_internal.json',
     ],
     'non_compiled_schema_files': [
     ],
     'main_non_compiled_schema_files': [
       'web_request_internal.json',
     ],
     # TODO(thestig) Do not include this file in non-extensions builds.
     # Then the conditional and else block can go away.
     # Do the same for extensions/common/api/schemas.gni.
     'conditions': [
       ['enable_extensions==1', {
         'non_compiled_schema_files': [
           '<@(main_non_compiled_schema_files)',
         ],
         'schema_files': [
           '<@(main_schema_files)',
         ],
       }, {
         'schema_files': [
         ],
       }],
     ],
     'cc_dir': 'extensions/common/api',
     'root_namespace': 'extensions::core_api::%(namespace)s',
     'impl_dir_': 'extensions/browser/api',
   },
 }