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

exercises/09_strings/strings1.rs

@@ -5,8 +5,6 @@
 // Execute `rustlings hint strings1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn main() {
     let answer = current_favorite_color();
     println!("My current favorite color is {}", answer);

exercises/09_strings/strings2.rs

@@ -5,8 +5,6 @@
 // Execute `rustlings hint strings2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn main() {
     let word = String::from("green"); // Try not changing this line :)
     if is_a_color_word(word) {

exercises/09_strings/strings3.rs

@@ -3,8 +3,6 @@
 // Execute `rustlings hint strings3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn trim_me(input: &str) -> String {
     // TODO: Remove whitespace from both ends of a string!
     ???

exercises/09_strings/strings4.rs

@@ -7,8 +7,6 @@
 //
 // No hints this time!
 
-// I AM NOT DONE
-
 fn string_slice(arg: &str) {
     println!("{}", arg);
 }