Comment removed in type bound

```rust
    type Err : Debug /*Display*/ + Reifiable + Clone;
```
...goes to:
```rust
    type Err: Debug + Reifiable + Clone;
```

...I agree that I probably should not have put a comment there, though

_Originally posted by @paulstansifer in https://github.com/rust-lang/rustfmt/issues/2781#issuecomment-507064482_