Use the AEC3 high-pass filter for the whole APM

This CL removes and replaces the legacy fixed-point high-pass filter in
APM with the floating point high-pass filter in AEC3.

Bug: webrtc:10907
Change-Id: I88cf8f622ab139e4ffa97f89a72425aa3becfc58
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150103
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28950}

modules/audio_processing/audio_buffer.h

@@ -32,6 +32,7 @@ enum Band { kBand0To8kHz = 0, kBand8To16kHz = 1, kBand16To24kHz = 2 };
 // operate on it in a controlled manner.
 class AudioBuffer {
  public:
+  static const int kSplitBandSize = 160;
   AudioBuffer(size_t input_rate,
               size_t input_num_channels,
               size_t buffer_rate,