AEC3: Add support in the echo subtractor for handling multiple channels

This CL adds support in the echo subtractor for handling multiple
capture and render channels.

The changes have passed bitexactness tests for substantial set
of mono recordings.

Bug: webrtc:10913
Change-Id: Ib448c9edf172ebc31e8c28db7b2f2a389a53adb9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/155168
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29389}

modules/audio_processing/test/echo_canceller_test_tools.h

@@ -15,7 +15,6 @@
 #include <vector>
 
 #include "api/array_view.h"
-#include "rtc_base/constructor_magic.h"
 #include "rtc_base/random.h"
 
 namespace webrtc {
@@ -41,7 +40,6 @@ class DelayBuffer {
  private:
   std::vector<T> buffer_;
   size_t next_insert_index_ = 0;
-  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(DelayBuffer);
 };
 
 }  // namespace webrtc