Disable HMM based transparent mode classifier

The HMM based transparent mode classifier is disabled until an issue
with diverging filters is resolved.

Bug: chromium:1155071
Change-Id: Iee249869f6ece1e48e834b3a4b9249c69a51286c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/196341
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32756}

modules/audio_processing/aec3/transparent_mode.cc

@@ -24,7 +24,9 @@ bool DeactivateTransparentMode() {
 }
 
 bool DeactivateTransparentModeHmm() {
-  return field_trial::IsEnabled("WebRTC-Aec3TransparentModeHmmKillSwitch");
+  // HMM based classifier is temporarily disabled (https://crbug.com/1155071).
+  return true;
+  // return field_trial::IsEnabled("WebRTC-Aec3TransparentModeHmmKillSwitch");
 }
 
 }  // namespace