Revert "Add one-stop-shop for built-in AEC toggling in APM"

This reverts commit 771b50ca0b92477ce8aabba025e959790dd1a949.

Reason for revert: Introduces error-prone config.

Original change's description:
> Add one-stop-shop for built-in AEC toggling in APM
> 
> This does not change what AEC functionality is available.
> However, a client that only uses this interface - and not the submodule
> pointer accessors - gets simpler code, and is guaranteed not to run any
> two AECs in tandem.
> 
> The submodule interface EchoControlMobile is being deprecated in
> https://webrtc-review.googlesource.com/c/src/+/89392
> 
> Bug: webrtc:9535
> Change-Id: Id9326074e566be6d8768010fc421c457beff402c
> Reviewed-on: https://webrtc-review.googlesource.com/89386
> Commit-Queue: Sam Zackrisson <saza@webrtc.org>
> Reviewed-by: Per Åhgren <peah@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#24066}

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

Change-Id: I43283a1b22538a4caa77313499989146b2ce67f1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9535
Reviewed-on: https://webrtc-review.googlesource.com/90060
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24067}

modules/audio_processing/audio_processing_impl.h

@@ -393,8 +393,6 @@ class AudioProcessingImpl : public AudioProcessing {
     int prev_analog_mic_level;
   } capture_ RTC_GUARDED_BY(crit_capture_);
 
-  // This struct requires EITHER crit_capture_ OR crit_render_ to read, and
-  // requires both locks to write.
   struct ApmCaptureNonLockedState {
     ApmCaptureNonLockedState(bool intelligibility_enabled)
         : capture_processing_format(kSampleRate16kHz),