Remove trait_alias, allow(incomplete_features).

trait_alias seems unused. no idea why it's there.

examples/std/src/bin/net.rs

@@ -1,5 +1,4 @@
 #![feature(type_alias_impl_trait)]
-#![allow(incomplete_features)]
 
 use clap::{AppSettings, Clap};
 use embassy::executor::{Executor, Spawner};

examples/std/src/bin/serial.rs

@@ -1,5 +1,4 @@
 #![feature(type_alias_impl_trait)]
-#![allow(incomplete_features)]
 
 #[path = "../serial_port.rs"]
 mod serial_port;

examples/std/src/bin/tick.rs

@@ -1,5 +1,4 @@
 #![feature(type_alias_impl_trait)]
-#![allow(incomplete_features)]
 
 use embassy::executor::Spawner;
 use embassy::time::{Duration, Timer};