Clean up and unify exercises

exercises/10_modules/modules1.rs

@@ -1,8 +1,3 @@
-// modules1.rs
-//
-// Execute `rustlings hint modules1` or use the `hint` watch subcommand for a
-// hint.
-
 mod sausage_factory {
     // Don't let anybody outside of this module see this!
     fn get_secret_recipe() -> String {

exercises/10_modules/modules2.rs

@@ -1,11 +1,6 @@
-// modules2.rs
-//
 // You can bring module paths into scopes and provide new names for them with
 // the 'use' and 'as' keywords. Fix these 'use' statements to make the code
 // compile.
-//
-// Execute `rustlings hint modules2` or use the `hint` watch subcommand for a
-// hint.
 
 mod delicious_snacks {
     // TODO: Fix these use statements

exercises/10_modules/modules3.rs

@@ -1,12 +1,7 @@
-// modules3.rs
-//
 // You can use the 'use' keyword to bring module paths from modules from
 // anywhere and especially from the Rust standard library into your scope. Bring
 // SystemTime and UNIX_EPOCH from the std::time module. Bonus style points if
 // you can do it with one line!
-//
-// Execute `rustlings hint modules3` or use the `hint` watch subcommand for a
-// hint.
 
 // TODO: Complete this use statement
 use ???