boxes: Move Rectangle.crop_and_scale to Mtk

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3501>

src/core/boxes-private.h

@@ -252,10 +252,4 @@ void meta_rectangle_transform (const MtkRectangle   *rect,
                                MetaMonitorTransform  transform,
                                int                   width,
                                int                   height,
-                               MtkRectangle         *dest);
-
-void meta_rectangle_crop_and_scale (const MtkRectangle *rect,
-                                    graphene_rect_t    *src_rect,
-                                    int                 dst_width,
-                                    int                 dst_height,
-                                    MtkRectangle       *dest);
+                               MtkRectangle         *dest);