Move AudioDecoder and related stuff to the api/ directory

BUG=webrtc:5805, webrtc:6725

Review-Url: https://codereview.webrtc.org/2668523004
Cr-Commit-Position: refs/heads/master@{#16534}
diff --git a/webrtc/tools/BUILD.gn b/webrtc/tools/BUILD.gn
index 46a0ede..169a7f4 100644
--- a/webrtc/tools/BUILD.gn
+++ b/webrtc/tools/BUILD.gn
@@ -208,7 +208,7 @@
       "../modules/audio_coding:ana_debug_dump_proto",
 
       # TODO(kwiberg): Remove this dependency.
-      "../modules/audio_coding:audio_format",
+      "../api/audio_codecs:audio_codecs_api",
       "../modules/congestion_controller",
       "../modules/rtp_rtcp",
       "../system_wrappers:system_wrappers_default",