Remove outdated TODO

Bug: webrtc:9535
Change-Id: I8f7a719eb9f32a91f45620453568e5f7d2264de8
Reviewed-on: https://webrtc-review.googlesource.com/c/109461
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25511}

modules/audio_processing/include/audio_processing.h

@@ -240,7 +240,6 @@ class AudioProcessing : public rtc::RefCountInterface {
   // by changing the default values in the AudioProcessing::Config struct.
   // The config is applied by passing the struct to the ApplyConfig method.
   struct Config {
-    // TODO(bugs.webrtc.org/9535): Currently unused. Use this to determine AEC.
     struct EchoCanceller {
       bool enabled = false;
       bool mobile_mode = false;