Injectable audio encoders: Moved audio encoder, factory and builtin factory to api/.

Plumbed AudioEncoderFactory up into CreatePeerConnectionFactory.

BUG=webrtc:5806

Review-Url: https://codereview.webrtc.org/2799033006
Cr-Original-Commit-Position: refs/heads/master@{#17977}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: eb1fde4a26f1a863c7488a63923eaf782c3ba177
diff --git a/call/BUILD.gn b/call/BUILD.gn
index 4111881..826ef65 100644
--- a/call/BUILD.gn
+++ b/call/BUILD.gn
@@ -29,8 +29,6 @@
     "../api/audio_codecs:audio_codecs_api",
     "../base:rtc_base",
     "../base:rtc_base_approved",
-    "../modules/audio_coding:audio_encoder_factory_interface",
-    "../modules/audio_coding:audio_encoder_interface",
   ]
 }
 
@@ -129,10 +127,10 @@
     deps = [
       ":call_interfaces",
       "..:webrtc_common",
+      "../api/audio_codecs:builtin_audio_encoder_factory",
       "../base:rtc_base_approved",
       "../logging:rtc_event_log_api",
       "../modules/audio_coding",
-      "../modules/audio_coding:builtin_audio_encoder_factory",
       "../modules/audio_mixer:audio_mixer_impl",
       "../modules/rtp_rtcp",
       "../system_wrappers",