Remove desugared async-trait example

Author: estebank

src/librustc_error_codes/error_codes/E0706.md

@@ -42,28 +42,7 @@ impl MyDatabase {
 
 Until these issues are resolved, you can use the [`async-trait` crate], allowing you to use
 `async fn` in traits by desugaring to "boxed futures"
-(`Pin<Box<dyn Future + Send + 'async>>`):
-
-```edition2018,ignore (example-of-desugaring-equivalence)
-#[async_trait]
-impl MyDatabase {
-    async fn get_user(&self) -> User {
-        unimplemented!()
-    }
-}
-
-// The annotated impl above gets desugared as follows:
-impl MyDatabase {
-    fn get_user<'async>(
-        &'async self,
-    ) -> Pin<Box<dyn std::future::Future<Output = User> + Send + 'async>>
-    where
-        Self: Sync + 'async,
-    {
-        unimplemented!()
-    }
-}
-```
+(`Pin<Box<dyn Future + Send + 'async>>`).
 
 Note that using these trait methods will result in a heap allocation per-function-call. This is not
 a significant cost for the vast majority of applications, but should be considered when deciding