Remove box syntax from rustc_ast

compiler/rustc_ast/src/lib.rs

@@ -8,7 +8,6 @@
     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
     test(attr(deny(warnings)))
 )]
-#![feature(box_syntax)]
 #![feature(box_patterns)]
 #![cfg_attr(bootstrap, feature(const_fn_transmute))]
 #![feature(crate_visibility_modifier)]

compiler/rustc_ast/src/ptr.rs

@@ -37,7 +37,7 @@ pub struct P<T: ?Sized> {
 /// Construct a `P<T>` from a `T` value.
 #[allow(non_snake_case)]
 pub fn P<T: 'static>(value: T) -> P<T> {
-    P { ptr: box value }
+    P { ptr: Box::new(value) }
 }
 
 impl<T: 'static> P<T> {