`unnecessary_conversion_for_trait` false positive

`unnecessary_conversion_for_trait` recommends to remove the `iter` in the call to `extend`. But then `xs` would be unavailable for the call to `println!`.
```rs
fn main() {
    let xs = vec![[0u8; 16]];
    let mut ys: Vec<[u8; 16]> = Vec::new();
    ys.extend(xs.iter());
    //          ^^^^^^^
    println!("{:?}", xs);
}
```