Remove unused members from `Viewport`

scene/main/viewport.h

@@ -260,11 +260,8 @@ private:
 	RID contact_3d_debug_multimesh;
 	RID contact_3d_debug_instance;
 
-	Rect2 last_vp_rect;
-
 	bool transparent_bg = false;
 	bool use_hdr_2d = false;
-	bool gen_mipmaps = false;
 
 	bool snap_controls_to_pixels = true;
 	bool snap_2d_transforms_to_pixel = false;