Remove deprecated setting for activating multichannel processing

Bug: webrtc:10859
Change-Id: I86cae6a9b765bc807c00632ec7d743b754941f81
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/160780
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29966}
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index 9ef4e26..539871d 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -261,10 +261,6 @@
       // Allow multi-channel processing of capture audio when AEC3 is active
       // or a custom AEC is injected..
       bool multi_channel_capture = false;
-
-      // Deprecated.
-      // TODO(peah): Remove.
-      bool experimental_multi_channel = false;
     } pipeline;
 
     // Enabled the pre-amplifier. It amplifies the capture signal