Clean up and unify exercises

exercises/15_traits/traits1.rs

@@ -1,11 +1,6 @@
-// traits1.rs
-//
 // Time to implement some traits! Your task is to implement the trait
 // `AppendBar` for the type `String`. The trait AppendBar has only one function,
 // which appends "Bar" to any object implementing this trait.
-//
-// Execute `rustlings hint traits1` or use the `hint` watch subcommand for a
-// hint.
 
 trait AppendBar {
     fn append_bar(self) -> Self;