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

exercises/01_variables/variables6.rs

@@ -3,8 +3,6 @@
 // Execute `rustlings hint variables6` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 const NUMBER = 3;
 fn main() {
     println!("Number {}", NUMBER);