rustc: Remove #![unstable] annotation

These are now no longer necessary with `-Z force-unstable-if-unmarked`

Author: alexcrichton

lib.rs

@@ -41,9 +41,6 @@
 //! [ti]: https://en.wikipedia.org/wiki/Terminfo
 
 #![crate_name = "term"]
-#![unstable(feature = "rustc_private",
-            reason = "use the crates.io `term` library instead",
-            issue = "27812")]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -54,13 +51,15 @@
 #![deny(missing_docs)]
 #![deny(warnings)]
 
-#![feature(box_syntax)]
 #![feature(staged_api)]
 #![cfg_attr(windows, feature(libc))]
 // Handle rustfmt skips
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 use std::io::prelude::*;
 
 pub use terminfo::TerminfoTerminal;