move track_audio_renderer.{cc,h} to private_renderer_webrtc_sources

This unbreaks the no-webrtc build after
https://codereview.chromium.org/1891183002

BUG=596174

Review URL: https://codereview.chromium.org/1888183003

Cr-Commit-Position: refs/heads/master@{#387688}
1 file changed