Remove redundant reference in closure with deref coercion

[semihbkgr]

In the explanation of deref coercion and turbofish, the &node introduces an extra level of indirection by taking a reference to &Node<T>. Since Rust's deref coercion can handle this automatically, the closure can be simplified to |node| node, allowing Rust to directly dereference the Box and return &Node<T>. I’m unsure whether this was added intentionally, but it was a part that confused me while reading.