Remove duplicate not done comment
As indicated in , I found it confusing to have 2 comments as the code wouldn't compile unless I solved both issues (I used the script from to remove a comment and use `:wn` to go to next exercise, hence this tripped me).
// Read more about them at https://doc.rust-lang.org/std/convert/trait.AsRef.html
// and https://doc.rust-lang.org/std/convert/trait.AsMut.html, respectively.
-// I AM NOT DONE
// Obtain the number of bytes (not characters) in the given argument
// Add the AsRef trait appropriately as a trait bound
fn byte_counter<T>(arg: T) -> usize {
