Remove trait_alias, allow(incomplete_features).

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

examples/stm32f0/src/bin/hello.rs

@@ -1,7 +1,6 @@
 #![no_std]
 #![no_main]
 #![feature(type_alias_impl_trait)]
-#![allow(incomplete_features)]
 
 use defmt::info;