Revert "Add core multi-channel pipeline in AEC3"

This reverts commit f3a197e55323aee974a932c52dd19fa88e5d4e38.

Reason for revert: Speculative revert, as this may'be broken some build bots

Original change's description:
> Add core multi-channel pipeline in AEC3
> This CL adds basic the basic pipeline to support multi-channel
> processing in AEC3.
> 
> Apart from that, it removes the 8 kHz processing support in several
> places of the AEC3 code.
> 
> Bug: webrtc:10913
> Change-Id: If5b75fa325ed0071deea94a7546cb4a7adf22137
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150332
> Commit-Queue: Per Ã…hgren <peah@webrtc.org>
> Reviewed-by: Sam Zackrisson <saza@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#29017}

TBR=saza@webrtc.org,peah@webrtc.org

Change-Id: I877d2993b9ccf024bd1d57bca1513c3e24d0bed3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:10913
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150940
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29022}
diff --git a/modules/audio_processing/audio_processing_impl.cc b/modules/audio_processing/audio_processing_impl.cc
index d639fd5..bc61b52 100644
--- a/modules/audio_processing/audio_processing_impl.cc
+++ b/modules/audio_processing/audio_processing_impl.cc
@@ -1849,8 +1849,7 @@
           echo_control_factory_->Create(proc_sample_rate_hz());
     } else {
       private_submodules_->echo_controller = absl::make_unique<EchoCanceller3>(
-          EchoCanceller3Config(), proc_sample_rate_hz(),
-          /*num_render_channels=*/1, /*num_capture_channels=*/1);
+          EchoCanceller3Config(), proc_sample_rate_hz());
     }
 
     capture_nonlocked_.echo_controller_enabled = true;