Stabilise then

compiler/rustc_index/src/lib.rs

@@ -1,5 +1,4 @@
 #![feature(allow_internal_unstable)]
-#![feature(bool_to_option)]
 #![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(extend_one)]

compiler/rustc_metadata/src/lib.rs

@@ -1,5 +1,4 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
-#![feature(bool_to_option)]
 #![feature(core_intrinsics)]
 #![feature(crate_visibility_modifier)]
 #![feature(drain_filter)]

compiler/rustc_parse/src/lib.rs

@@ -1,6 +1,5 @@
 //! The main parser interface.
 
-#![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
 #![feature(bindings_after_at)]
 #![feature(iter_order_by)]