Clean up and unify exercises

exercises/17_tests/tests3.rs

@@ -1,11 +1,6 @@
-// tests3.rs
-//
 // This test isn't testing our function -- make it do that in such a way that
 // the test passes. Then write a second test that tests whether we get the
 // result we expect to get when we call `is_even(5)`.
-//
-// Execute `rustlings hint tests3` or use the `hint` watch subcommand for a
-// hint.
 
 pub fn is_even(num: i32) -> bool {
     num % 2 == 0