Stabilize async closures

Author: compiler-errors

tests/pass/async-closure-captures.rs

@@ -1,6 +1,6 @@
 // Same as rustc's `tests/ui/async-await/async-closures/captures.rs`, keep in sync
 
-#![feature(async_closure, async_trait_bounds)]
+#![feature(async_trait_bounds)]
 
 use std::future::Future;
 use std::pin::pin;

tests/pass/async-closure-drop.rs

@@ -1,4 +1,4 @@
-#![feature(async_closure, async_trait_bounds)]
+#![feature(async_fn_traits, async_trait_bounds)]
 
 use std::future::Future;
 use std::pin::pin;

tests/pass/async-closure.rs

@@ -1,4 +1,4 @@
-#![feature(async_closure, async_fn_traits)]
+#![feature(async_fn_traits)]
 #![allow(unused)]
 
 use std::future::Future;

tests/pass/async-drop.rs

@@ -6,7 +6,7 @@
 // please consider modifying rustc's async drop test at
 // `tests/ui/async-await/async-drop.rs`.
 
-#![feature(async_drop, impl_trait_in_assoc_type, async_closure)]
+#![feature(async_drop, impl_trait_in_assoc_type)]
 #![allow(incomplete_features, dead_code)]
 
 // FIXME(zetanumbers): consider AsyncDestruct::async_drop cleanup tests