Remove no-longer used `IdFunctor::map_id`

compiler/rustc_data_structures/src/functor.rs

@@ -4,14 +4,6 @@ use std::mem;
 pub trait IdFunctor: Sized {
     type Inner;
 
-    #[inline]
-    fn map_id<F>(self, mut f: F) -> Self
-    where
-        F: FnMut(Self::Inner) -> Self::Inner,
-    {
-        self.try_map_id::<_, !>(|value| Ok(f(value))).into_ok()
-    }
-
     fn try_map_id<F, E>(self, f: F) -> Result<Self, E>
     where
         F: FnMut(Self::Inner) -> Result<Self::Inner, E>;

compiler/rustc_data_structures/src/lib.rs

@@ -25,7 +25,6 @@
 #![feature(once_cell)]
 #![feature(test)]
 #![feature(thread_id_value)]
-#![feature(unwrap_infallible)]
 #![allow(rustc::default_hash_types)]
 #![deny(unaligned_references)]