Media Remoting: Remove old interstitial implementation.

media/base/media_observer.h

Index: media/base/media_observer.h
diff --git a/media/base/media_observer.h b/media/base/media_observer.h
index 0181b1d00be6b41f47d8f6ccd44c55cda4ad5685..4bb3366cde965c95747c9e1d65de3131ce0168d2 100644
--- a/media/base/media_observer.h
+++ b/media/base/media_observer.h
@@ -56,10 +56,6 @@ class MEDIA_EXPORT MediaObserver {
   virtual void OnPlaying() = 0;
   virtual void OnPaused() = 0;
 
-  // Called when a poster image URL is set, which happens when media is loaded
-  // or the poster attribute is changed.
-  virtual void OnSetPoster(const GURL& poster) = 0;
-
   // Set the MediaObserverClient.
   virtual void SetClient(MediaObserverClient* client) = 0;
 };