Ch. 17: drop lifetime not required in 2024 Edition

This makes for a nicely simpler introduction of this feature!

src/ch17-01-futures-and-syntax.md

@@ -153,15 +153,15 @@ anonymous data type the compiler creates for that async block.
 
 Thus, writing `async fn` is equivalent to writing a function which returns a
 *future* of the return type. When the compiler sees a function definition such
-as the `async fn page_title` in Listing 17-1, it’s equivalent to a non-async
+as the `async fn page_title` in Listing 17-2, it’s equivalent to a non-async
 function defined like this:
 
 ```rust
 # extern crate trpl; // required for mdbook test
 use std::future::Future;
 use trpl::Html;
 
-fn page_title(url: &str) -> impl Future<Output = Option<String>> + '_ {
+fn page_title(url: &str) -> impl Future<Output = Option<String>> {
     async move {
         let text = trpl::get(url).await.text().await;
         Html::parse(&text)
@@ -187,13 +187,6 @@ Let’s walk through each part of the transformed version:
 * The new function body is an `async move` block because of how it uses the
   `url` parameter. (We’ll talk about `async` vs. `async move` much more later
   in the chapter.)
-* The new version of the function has a kind of lifetime we haven’t seen before
-  in the output type: `'_`. Because the function returns a `Future` which refers
-  to a reference—in this case, the reference from the `url` parameter—we need to
-  tell Rust that we mean for that reference to be included. We don’t have to
-  name the lifetime here, because Rust is smart enough to know there is only one
-  reference which could be involved, but we *do* have to be explicit that the
-  resulting `Future` is bound by that lifetime.
 
 Now we can call `page_title` in `main`. To start, we’ll just get the title
 for a single page. In Listing 17-3, we follow the same pattern we used for