Update Copy/Clone documentation WRT arrays

compiler/rustc_error_codes/src/error_codes/E0206.md

@@ -4,15 +4,12 @@ enum.
 Erroneous code example:
 
 ```compile_fail,E0206
-type Foo = [u8; 256];
-impl Copy for Foo { } // error!
-
 #[derive(Copy, Clone)]
 struct Bar;
 
 impl Copy for &'static mut Bar { } // error!
 ```
 
-You can only implement `Copy` for a struct or an enum. Both of the previous
-examples will fail, because neither `[u8; 256]` nor `&'static mut Bar`
-(mutable reference to `Bar`) is a struct or enum.
+You can only implement `Copy` for a struct or an enum.
+The previous example will fail because `&'static mut Bar`
+is not a struct or enum.