Tracking issue for inclusion of `derive` in lint `unused_attributes`

The following code emits an unsquelchable warning.

```
#![crate_type="lib"]

#[derive()]
struct Struct;
```

```
warning: empty trait list in `derive`
 --> src/lib.rs:4:1
  |
4 | #[derive()]
  | ^^^^^^^^^^^
```

~~This warning should have a named lint `unused_derive` that is a part of the `unused` group of lints.~~

This warning should be a part of `unused_attributes`.
