Reimplement the builtin audio codec factories using the new stuff in api/

webrtc/api/audio_codecs/test/BUILD.gn

 # Copyright (c) 2017 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.
 
 import("../../../webrtc.gni")
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
 
 if (rtc_include_tests) {
   rtc_source_set("audio_codecs_api_unittests") {
     testonly = true
     sources = [
       "audio_decoder_factory_template_unittest.cc",
       "audio_encoder_factory_template_unittest.cc",
     ]
     deps = [
       "..:audio_codecs_api",
-      "../../../rtc_base:protobuf_utils",  # TODO(kwiberg): Why is this needed?
       "../../../rtc_base:rtc_base_approved",
       "../../../test:audio_codec_mocks",
       "../../../test:test_support",
       "../L16:audio_decoder_L16",
       "../L16:audio_encoder_L16",
       "../g711:audio_decoder_g711",
       "../g711:audio_encoder_g711",
       "../g722:audio_decoder_g722",
       "../g722:audio_encoder_g722",
       "../ilbc:audio_decoder_ilbc",
       "../ilbc:audio_encoder_ilbc",
       "../isac:audio_decoder_isac_fix",
       "../isac:audio_decoder_isac_float",
       "../isac:audio_encoder_isac_fix",
       "../isac:audio_encoder_isac_float",
       "../opus:audio_decoder_opus",
       "../opus:audio_encoder_opus",
       "//testing/gmock",
     ]
   }
 }