Stabilize ::{core,std}::pin::pin!

Author: danielhenrymantilla

tests/pass/issues/issue-miri-2068.rs

@@ -1,5 +1,3 @@
-#![feature(pin_macro)]
-
 use core::future::Future;
 use core::pin::Pin;
 use core::task::{Context, Poll};

tests/pass/stacked-borrows/future-self-referential.rs

@@ -1,5 +1,3 @@
-#![feature(pin_macro)]
-
 use std::future::*;
 use std::marker::PhantomPinned;
 use std::pin::*;