chore: remove async-std leftovers

Pull-Request: #6075.

Author: jxs

transports/quic/tests/smoke.rs

@@ -41,12 +41,6 @@ async fn tokio_smoke() {
     smoke::<quic::tokio::Provider>().await
 }
 
-#[cfg(feature = "tokio")]
-#[tokio::test]
-async fn async_std_smoke() {
-    smoke::<quic::tokio::Provider>().await
-}
-
 #[cfg(feature = "tokio")]
 #[tokio::test]
 async fn endpoint_reuse() {

transports/websocket/src/quicksink.rs

@@ -17,8 +17,8 @@
 // # Examples
 //
 // ```no_run
-// use async_std::io;
 // use futures::prelude::*;
+// use tokio::io;
 //
 // use crate::quicksink::Action;
 //