Remove an unused method in NetEq::Expand

TBR=ivoc@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/53549004

Cr-Commit-Position: refs/heads/master@{#9292}
diff --git a/webrtc/modules/audio_coding/neteq/expand.h b/webrtc/modules/audio_coding/neteq/expand.h
index 674813f..5679ec1 100644
--- a/webrtc/modules/audio_coding/neteq/expand.h
+++ b/webrtc/modules/audio_coding/neteq/expand.h
@@ -54,12 +54,6 @@
   // a period of expands.
   virtual void SetParametersForMergeAfterExpand();
 
-  // Sets the mute factor for |channel| to |value|.
-  void SetMuteFactor(int16_t value, size_t channel) {
-    assert(channel < num_channels_);
-    channel_parameters_[channel].mute_factor = value;
-  }
-
   // Returns the mute factor for |channel|.
   int16_t MuteFactor(size_t channel) {
     assert(channel < num_channels_);