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 Ã…hgren <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}
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index b543b6c..9d27f16 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -253,13 +253,6 @@
   // by changing the default values in the AudioProcessing::Config struct.
   // The config is applied by passing the struct to the ApplyConfig method.
   struct Config {
-    // Configures whether acoustic echo cancellation is performed.
-    // Has a specific tuning for mobile devices.
-    struct EchoCancellation {
-      bool enabled = false;
-      bool mobile_mode = false;
-    } echo_cancellation;
-
     struct ResidualEchoDetector {
       bool enabled = true;
     } residual_echo_detector;
@@ -803,7 +796,7 @@
 class EchoCancellation {
  public:
   // EchoCancellation and EchoControlMobile may not be enabled simultaneously.
-  // If both are enabled, one (unspecified) will automatically be disabled.
+  // Enabling one will disable the other.
   virtual int Enable(bool enable) = 0;
   virtual bool is_enabled() const = 0;
 
@@ -907,7 +900,7 @@
 class EchoControlMobile {
  public:
   // EchoCancellation and EchoControlMobile may not be enabled simultaneously.
-  // If both are enabled, one (unspecified) will automatically be disabled.
+  // Enabling one will disable the other.
   virtual int Enable(bool enable) = 0;
   virtual bool is_enabled() const = 0;