### What it does
Checks for `let _ = <expr>` where expr is `#[must_use]`

### Why is this bad?
It's better to explicitly handle the value of a `#[must_use]`
expr

### Example
```
fn f() -> Result<u32, u32> {
    Ok(0)
}

let _ = f();
// is_ok() is marked #[must_use]
let _ = f().is_ok();
```