Rust warning「warning: variable does not need to be mutable」が発生した場合の対処法

fn main() {

    let mut str: String = "hello".to_string();

    println!("{}", str);

}

warning: variable does not need to be mutable
 --> sample.rs:3:9
  |
3 |     let mut str: String = "hello".to_string();
  |         ----^^^
  |         |
  |         help: remove this `mut`
  |
  = note: `#[warn(unused_mut)]` on by default

warning: 1 warning emitted

fn main() {

    let mut str: String = "hello".to_string();

    println!("{}", str);

}