Drop Scene::ImageFilterType

It's unused, GL_LINEAR filter is used by default now.

src/scene.cpp

@@ -593,7 +593,6 @@ PlatformSurfaceTexture *Scene::createPlatformSurfaceTextureWayland(SurfacePixmap
 Scene::Window::Window(Toplevel *client, QObject *parent)
     : QObject(parent)
     , toplevel(client)
-    , filter(ImageFilterFast)
     , disable_painting(0)
 {
     if (qobject_cast<WaylandClient *>(client)) {

src/scene.h

@@ -131,11 +131,6 @@ public:
         PAINT_WINDOW_LANCZOS = 1 << 8
         // PAINT_SCREEN_WITH_TRANSFORMED_WINDOWS_WITHOUT_FULL_REPAINTS = 1 << 9 has been removed
     };
-    // types of filtering available
-    enum ImageFilterType {
-        ImageFilterFast,
-        ImageFilterGood,
-    };
     virtual OverlayWindow* overlayWindow() const = 0;
 
     virtual bool makeOpenGLContextCurrent();
@@ -339,7 +334,6 @@ public:
 
 protected:
     Toplevel* toplevel;
-    ImageFilterType filter;
 private:
     void referencePreviousPixmap_helper(SurfaceItem *item);
     void unreferencePreviousPixmap_helper(SurfaceItem *item);