Move CNG and RED management into the Rent-A-Codec

This leaves CodecOwner without a job, so we eliminate it.

BUG=webrtc:5028

Review URL: https://codereview.webrtc.org/1443653004

Cr-Commit-Position: refs/heads/master@{#10650}

webrtc/modules/audio_coding/BUILD.gn

@@ -63,8 +63,6 @@ source_set("audio_coding") {
     "main/acm2/call_statistics.h",
     "main/acm2/codec_manager.cc",
     "main/acm2/codec_manager.h",
-    "main/acm2/codec_owner.cc",
-    "main/acm2/codec_owner.h",
     "main/acm2/initial_delay_manager.cc",
     "main/acm2/initial_delay_manager.h",
     "main/include/audio_coding_module.h",