Clean up and unify exercises

exercises/07_structs/structs3.rs

@@ -1,11 +1,6 @@
-// structs3.rs
-//
 // Structs contain data, but can also have logic. In this exercise we have
 // defined the Package struct and we want to test some logic attached to it.
 // Make the code compile and the tests pass!
-//
-// Execute `rustlings hint structs3` or use the `hint` watch subcommand for a
-// hint.
 
 #[derive(Debug)]
 struct Package {