Inherit EventTarget interface instead of duplicating its code

Source/modules/mediastream/MediaStreamTrack.idl

 /*
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 [
-    EventTarget,
     ActiveDOMObject
-] interface MediaStreamTrack {
+] interface MediaStreamTrack : EventTarget {
     readonly attribute DOMString kind;
     readonly attribute DOMString id;
     readonly attribute DOMString label;
              attribute boolean enabled;
 
     readonly attribute DOMString readyState;
 
     attribute EventListener onmute;
     attribute EventListener onunmute;
     attribute EventListener onended;
 
     [CallWith=ScriptExecutionContext, RaisesException] static void getSources(MediaStreamTrackSourcesCallback callback);
-
-    // EventTarget interface
-    void addEventListener(DOMString type,
-                          EventListener listener,
-                          optional boolean useCapture);
-    void removeEventListener(DOMString type,
-                             EventListener listener,
-                             optional boolean useCapture);
-    [RaisesException] boolean dispatchEvent(Event event);
 };