Drop unused showingTrackWithSameKind declaration from HTMLMediaElement

Review URL: https://codereview.chromium.org/1304183003

git-svn-id: svn://svn.chromium.org/blink/trunk@200985 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/html/HTMLMediaElement.h

@@ -381,8 +381,6 @@ private:
     void executeDeferredLoad();
     void deferredLoadTimerFired(Timer<HTMLMediaElement>*);
 
-    HTMLTrackElement* showingTrackWithSameKind(HTMLTrackElement*) const;
-
     void markCaptionAndSubtitleTracksAsUnconfigured();
 
     // This does not check user gesture restrictions.