GN: Update audio_sink.h location

This should have been a part of
https://codereview.webrtc.org/1740873003/
but wasn't discovered since we cannot have --check turned
on for GN yet.

BUG=webrtc:5589
TBR=solenberg@webrtc.org, henrika@webrtc.org,

Review URL: https://codereview.webrtc.org/1744123002 .

Cr-Commit-Position: refs/heads/master@{#11803}

webrtc/BUILD.gn

@@ -228,6 +228,7 @@ if (!build_with_chromium) {
 
 source_set("webrtc_common") {
   sources = [
+    "audio_sink.h",
     "common_types.cc",
     "common_types.h",
     "config.cc",

webrtc/audio/BUILD.gn

@@ -14,7 +14,6 @@ source_set("audio") {
     "audio_receive_stream.h",
     "audio_send_stream.cc",
     "audio_send_stream.h",
-    "audio_sink.h",
     "audio_state.cc",
     "audio_state.h",
     "conversion.h",