Remove nightly features in rustc_type_ir

compiler/rustc_index/src/vec.rs

@@ -124,15 +124,17 @@ macro_rules! newtype_index {
 
             #[inline]
             $v const fn from_usize(value: usize) -> Self {
-                assert!(value <= ($max as usize));
+                // FIXME: replace with `assert!(value <= ($max as usize));` once `const_panic` is stable
+                [()][(value > ($max as usize)) as usize];
                 unsafe {
                     Self::from_u32_unchecked(value as u32)
                 }
             }
 
             #[inline]
             $v const fn from_u32(value: u32) -> Self {
-                assert!(value <= $max);
+                // FIXME: replace with `assert!(value <= $max);` once `const_panic` is stable
+                [()][(value > $max) as usize];
                 unsafe {
                     Self::from_u32_unchecked(value)
                 }

compiler/rustc_type_ir/src/lib.rs

@@ -1,7 +1,3 @@
-#![feature(never_type)]
-#![feature(const_panic)]
-#![feature(control_flow_enum)]
-
 #[macro_use]
 extern crate bitflags;
 #[macro_use]