cleanup: s/impl Copy/#[derive(Copy)]/g
@@ -1680,8 +1680,8 @@ specific type.
Implementations are defined with the keyword `impl`.
```
+# #[derive(Copy)]
# struct Point {x: f64, y: f64};
-# impl Copy for Point {}
# type Surface = i32;
# struct BoundingBox {x: f64, y: f64, width: f64, height: f64};
# trait Shape { fn draw(&self, Surface); fn bounding_box(&self) -> BoundingBox; }
