Remove all references to GYP

webrtc/modules/audio_mixer/audio_mixer.gypi

-# Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
-#
-# Use of this source code is governed by a BSD-style license
-# that can be found in the LICENSE file in the root of the source
-# tree. An additional intellectual property rights grant can be found
-# in the file PATENTS.  All contributing project authors may
-# be found in the AUTHORS file in the root of the source tree.
-
-{
-  'targets': [
-    {
-      'target_name': 'audio_mixer_impl',
-      'type': 'static_library',
-      'dependencies': [
-        'audio_frame_manipulator',
-        'audio_processing',
-        'webrtc_utility',
-        '<(webrtc_root)/api/api.gyp:audio_mixer_api',
-        '<(webrtc_root)/base/base.gyp:rtc_base_approved',
-        '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
-      ],
-      'sources': [
-        'audio_mixer_impl.cc',
-        'audio_mixer_impl.h',
-      ],
-    },
-    {
-      'target_name': 'audio_frame_manipulator',
-      'type': 'static_library',
-      'dependencies': [
-          'webrtc_utility',
-          '<(webrtc_root)/base/base.gyp:rtc_base_approved',
-      ],
-      'sources': [
-        'audio_frame_manipulator.cc',
-        'audio_frame_manipulator.h',
-      ],
-    },
-  ], # targets
-}