Clean up and unify exercises

exercises/quiz3.rs

@@ -1,5 +1,3 @@
-// quiz3.rs
-//
 // This quiz tests:
 // - Generics
 // - Traits
@@ -13,8 +11,6 @@
 // Make the necessary code changes in the struct ReportCard and the impl block
 // to support alphabetical report cards. Change the Grade in the second test to
 // "A+" to show that your changes allow alphabetical grades.
-//
-// Execute `rustlings hint quiz3` or use the `hint` watch subcommand for a hint.
 
 pub struct ReportCard {
     pub grade: f32,