Revert "IWYU: Add <math.h> for fabsf() and powf()"

This reverts commit 7d47525e8bc11d0e401c2180e0222c1858f8e134.

Reason for revert: breaking downstream projects

Original change's description:
> IWYU: Add <math.h> for fabsf() and powf()
> 
> Fix the build with libstdc++ after 496cedfe5 ("AEC3: Reverberation model:
> Changes on the decay estimation") by including the missing header:
> 
>     ../../modules/audio_processing/aec3/reverb_model_estimator.cc: In constructor ‘webrtc::ReverbModelEstimator::ReverbModelEstimator(const webrtc::EchoCanceller3Config&)’:
>     ../../modules/audio_processing/aec3/reverb_model_estimator.cc:61:21: error: ‘fabsf’ was not declared in this scope
>            reverb_decay_(fabsf(config.ep_strength.default_len)),
>                          ^~~~~
>     ../../modules/audio_processing/aec3/reverb_model_estimator.cc:61:21: note: suggested alternative: ‘labs’
>            reverb_decay_(fabsf(config.ep_strength.default_len)),
>                          ^~~~~
>                          labs
>     ../../modules/audio_processing/aec3/reverb_model_estimator.cc: In member function ‘void webrtc::ReverbModelEstimator::UpdateReverbDecay(const std::vector<float>&)’:
>     ../../modules/audio_processing/aec3/reverb_model_estimator.cc:206:15: error: ‘powf’ was not declared in this scope
>            decay = powf(2.0f, -exp_candidate * kFftLengthBy2);
>                    ^~~~
> 
> Spotted by Jose Dapena Paz <jose.dapena@lge.com>.
> 
> Bug: chromium:819294
> Change-Id: If992e5e473b9d4d0c1b3c1006c3816b7c4eee296
> Reviewed-on: https://webrtc-review.googlesource.com/87241
> Reviewed-by: Jesus de Vicente Pena <devicentepena@webrtc.org>
> Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
> Commit-Queue: Raphael Kubo da Costa (rakuco) <raphael.kubo.da.costa@intel.com>
> Cr-Commit-Position: refs/heads/master@{#23863}

TBR=gustaf@webrtc.org,alessiob@webrtc.org,raphael.kubo.da.costa@intel.com,devicentepena@webrtc.org

Change-Id: I8adcec57d67de2efcbf0ebef0cdb700fcc21689a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:819294
Reviewed-on: https://webrtc-review.googlesource.com/87400
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23864}
diff --git a/modules/audio_processing/aec3/reverb_model_estimator.cc b/modules/audio_processing/aec3/reverb_model_estimator.cc
index 39cb580..18b2a84 100644
--- a/modules/audio_processing/aec3/reverb_model_estimator.cc
+++ b/modules/audio_processing/aec3/reverb_model_estimator.cc
@@ -10,8 +10,6 @@
 
 #include "modules/audio_processing/aec3/reverb_model_estimator.h"
 
-#include <math.h>
-
 #include <algorithm>
 #include <array>
 #include <memory>