Remove EffectFrame leftovers in Scene

(cherry picked from commit e3da5fc7)

src/scene.h

@@ -31,7 +31,6 @@ class DecoratedClientImpl;
 class Output;
 class DecorationRenderer;
 class Deleted;
-class EffectFrameImpl;
 class EffectWindowImpl;
 class GLTexture;
 class Item;
@@ -75,7 +74,6 @@ class KWIN_EXPORT Scene : public QObject
 public:
     explicit Scene(QObject *parent = nullptr);
     ~Scene() override;
-    class EffectFrame;
 
     void initialize();
 

src/scenes/opengl/scene_opengl.h

@@ -49,7 +49,6 @@ public:
         const bool hardwareClipping;
     };
 
-    class EffectFrame;
     explicit SceneOpenGL(OpenGLBackend *backend, QObject *parent = nullptr);
     ~SceneOpenGL() override;
     bool initFailed() const override;