Remove media::FilterCollection::Clear() because no one calls it.

media/base/filter_collection.cc

Index: media/base/filter_collection.cc
diff --git a/media/base/filter_collection.cc b/media/base/filter_collection.cc
index 6bba99ec90ae16e7602c09fa03fc5bc97f59b790..911edd5832cd6150b57283af53f80eeed9df8f9a 100644
--- a/media/base/filter_collection.cc
+++ b/media/base/filter_collection.cc
@@ -41,9 +41,4 @@ scoped_ptr<VideoRenderer> FilterCollection::GetVideoRenderer() {
   return video_renderer_.Pass();
 }
 
-void FilterCollection::Clear() {
-  audio_renderer_.reset();
-  video_renderer_.reset();
-}
-
 }  // namespace media