NetEQ: GenerateBackgroundNoise moved to BackgrounNoise

Bug: webrtc:10548
Change-Id: Ie9da0755793078b81c60c3751abcbff13da40ede
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/132788
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27619}

modules/audio_coding/neteq/expand.h

@@ -76,13 +76,6 @@ class Expand {
                             size_t length,
                             int16_t* random_vector);
 
-  void GenerateBackgroundNoise(int16_t* random_vector,
-                               size_t channel,
-                               int mute_slope,
-                               bool too_many_expands,
-                               size_t num_noise_samples,
-                               int16_t* buffer);
-
   // Initializes member variables at the beginning of an expand period.
   void InitializeForAnExpandPeriod();