Removes Set/GetRecordingChannel() from the ADM

These two unused APIs are removed:

SetRecordingChannel(const ChannelType channel)
RecordingChannel(ChannelType* channel) const

Bug: webrtc:7306
Change-Id: I3289c4b9a5eebb64cc0aa3a1c1144e9c4d6a661d
Reviewed-on: https://webrtc-review.googlesource.com/22681
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Commit-Queue: Henrik Andreassson <henrika@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20667}
diff --git a/media/engine/adm_helpers.cc b/media/engine/adm_helpers.cc
index 3a1776e..b973ce6 100644
--- a/media/engine/adm_helpers.cc
+++ b/media/engine/adm_helpers.cc
@@ -42,10 +42,7 @@
     return;
   }
 
-  // Set device and stereo mode.
-  if (adm->SetRecordingChannel(AudioDeviceModule::kChannelBoth) != 0) {
-    RTC_LOG(LS_ERROR) << "Unable to set recording channel to kChannelBoth.";
-  }
+  // Set device to default.
   if (adm->SetRecordingDevice(AUDIO_DEVICE_ID) != 0) {
     RTC_LOG(LS_ERROR) << "Unable to set recording device.";
     return;