Remove "I AM NOT DONE" and the verify mode and add AppState

exercises/01_variables/variables3.rs

@@ -3,8 +3,6 @@
 // Execute `rustlings hint variables3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn main() {
     let x: i32;
     println!("Number {}", x);