Clean up and unify exercises

exercises/16_lifetimes/lifetimes1.rs

@@ -1,12 +1,7 @@
-// lifetimes1.rs
-//
 // The Rust compiler needs to know how to check whether supplied references are
 // valid, so that it can let the programmer know if a reference is at risk of
 // going out of scope before it is used. Remember, references are borrows and do
 // not own their own data. What if their owner goes out of scope?
-//
-// Execute `rustlings hint lifetimes1` or use the `hint` watch subcommand for a
-// hint.
 
 fn longest(x: &str, y: &str) -> &str {
     if x.len() > y.len() {

exercises/16_lifetimes/lifetimes2.rs

@@ -1,10 +1,5 @@
-// lifetimes2.rs
-//
 // So if the compiler is just validating the references passed to the annotated
 // parameters and the return type, what do we need to change?
-//
-// Execute `rustlings hint lifetimes2` or use the `hint` watch subcommand for a
-// hint.
 
 fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
     if x.len() > y.len() {

exercises/16_lifetimes/lifetimes3.rs

@@ -1,9 +1,4 @@
-// lifetimes3.rs
-//
 // Lifetimes are also needed when structs hold references.
-//
-// Execute `rustlings hint lifetimes3` or use the `hint` watch subcommand for a
-// hint.
 
 struct Book {
     author: &str,
@@ -13,7 +8,10 @@ struct Book {
 fn main() {
     let name = String::from("Jill Smith");
     let title = String::from("Fish Flying");
-    let book = Book { author: &name, title: &title };
+    let book = Book {
+        author: &name,
+        title: &title,
+    };
 
     println!("{} by {}", book.title, book.author);
 }