Inherit EventTarget interface instead of duplicating its code

Source/bindings/tests/idls/TestEventTarget.idl

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 [
-    EventTarget,
     MasqueradesAsUndefined
-] interface TestEventTarget {
+] interface TestEventTarget : EventTarget {
 
     getter Node item([IsIndex] unsigned long index);
     [ImplementedAs=anonymousIndexedSetter] setter Node (unsigned long index, Node node);
     getter Node namedItem(DOMString name);
     [ImplementedAs=anonymousNamedSetter] setter Node(DOMString name, [TreatUndefinedAs=anonymousNamedSetterUndefined] DOMString value);
     [ImplementedAs=anonymousIndexedDeleter, RaisesException] deleter boolean(unsigned long index);
     [ImplementedAs=anonymousNamedDeleter] deleter boolean(DOMString name);
-
-    void addEventListener(DOMString type, 
-                          EventListener listener, 
-                          optional boolean useCapture);
-    void removeEventListener(DOMString type, 
-                             EventListener listener, 
-                             optional boolean useCapture);
-    [RaisesException] boolean dispatchEvent(Event evt);
 };