Remove decl for undefined&unused MediaKeySession::enqueueEvent() method.

Source/modules/encryptedmedia/MediaKeySession.h

 /*
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 63 matching lines @@
     ScriptPromise closed(ScriptState*);
     MediaKeyStatusMap* keyStatuses();
 
     ScriptPromise generateRequest(ScriptState*, const String& initDataType, const DOMArrayPiece& initData);
     ScriptPromise load(ScriptState*, const String& sessionId);
 
     ScriptPromise update(ScriptState*, const DOMArrayPiece& response);
     ScriptPromise close(ScriptState*);
     ScriptPromise remove(ScriptState*);
 
-    void enqueueEvent(PassRefPtrWillBeRawPtr<Event>);
-
     // EventTarget
     virtual const AtomicString& interfaceName() const override;
     virtual ExecutionContext* executionContext() const override;
 
     // ActiveDOMObject
     virtual bool hasPendingActivity() const override;
     virtual void stop() override;
 
     DECLARE_VIRTUAL_TRACE();
 
@@ skipping 39 matching lines @@
     typedef ScriptPromiseProperty<Member<MediaKeySession>, ToV8UndefinedGenerator, RefPtrWillBeMember<DOMException>> ClosedPromise;
     Member<ClosedPromise> m_closedPromise;
 
     HeapDeque<Member<PendingAction>> m_pendingActions;
     Timer<MediaKeySession> m_actionTimer;
 };
 
 } // namespace blink
 
 #endif // MediaKeySession_h