Clean up and unify exercises

exercises/08_enums/enums1.rs

@@ -1,7 +1,3 @@
-// enums1.rs
-//
-// No hints this time! ;)
-
 #[derive(Debug)]
 enum Message {
     // TODO: define a few types of messages as used below

exercises/08_enums/enums2.rs

@@ -1,8 +1,3 @@
-// enums2.rs
-//
-// Execute `rustlings hint enums2` or use the `hint` watch subcommand for a
-// hint.
-
 #[derive(Debug)]
 enum Message {
     // TODO: define the different variants used below

exercises/08_enums/enums3.rs

@@ -1,9 +1,4 @@
-// enums3.rs
-//
 // Address all the TODOs to make the tests pass!
-//
-// Execute `rustlings hint enums3` or use the `hint` watch subcommand for a
-// hint.
 
 enum Message {
     // TODO: implement the message variant types based on their usage below