Remove all AudioBuffer code that is not related to storing audio data

This CL moves/removes all code from the AudioBuffer that:
-Is not directly handling audio data (e.g., keytaps, VAD descisions).
-Is caching aggregated versions of the rest of the audio data.
-Is not used (or only used in testing)

Bug: webrtc:10882
Change-Id: I737deb3f692748eff30f46ad806b2c6f6292802c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/149072
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Commit-Queue: Per Åhgren <peah@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28866}

modules/audio_processing/audio_processing_impl.h

@@ -394,6 +394,12 @@ class AudioProcessingImpl : public AudioProcessing {
     int playout_volume;
     int prev_playout_volume;
     AudioProcessingStats stats;
+    struct KeyboardInfo {
+      void Extract(const float* const* data, const StreamConfig& stream_config);
+      size_t num_keyboard_frames = 0;
+      const float* keyboard_data = nullptr;
+    } keyboard_info;
+    AudioFrame::VADActivity vad_activity = AudioFrame::kVadUnknown;
   } capture_ RTC_GUARDED_BY(crit_capture_);
 
   struct ApmCaptureNonLockedState {