refactor(app/test): remove duplicate io reëxport

the same `pub use` bundle is found in the parent `lib.rs`.

this removes it, and refers to the same `mod io {}` defined above.

linkerd/app/test/src/connect.rs

@@ -1,3 +1,4 @@
+use crate::io;
 use linkerd_app_core::{
     svc::{Param, Service},
     transport::{ClientAddr, Local, Remote, ServerAddr},
@@ -14,11 +15,6 @@ use std::{
 };
 use tracing::instrument::{Instrument, Instrumented};
 
-mod io {
-    pub use linkerd_app_core::io::*;
-    pub use tokio_test::io::*;
-}
-
 type ConnectFn<T> = Box<dyn FnMut(T) -> ConnectFuture + Send>;
 
 pub type ConnectFuture =