rust private

rustdoc: Hide `self: Box<Self>` in list of deref methods These methods can never be called through deref so there is no point including them. For example you can't call [`into_boxed_bytes`](https://doc.rust-lang.org/nightly/std/string/struct.String.html#method.into_boxed_bytes) or [`into_string`](https://doc.rust-lang.org/nightly/std/string/struct.String.html#method.into_string) on `String`.