tidy/features: fix checking of lang features

Removes the `STATUSES` static which duplicates truth from the pattern
match in `collect_lang_features`.

Fixes existing duplicates by renaming:
- never_type{,_impls} on `impl`s on `!`
- concat_idents{,_macro} on `macro_rules! concat_idents`

Fixes #37013.

src/libstd/macros.rs

@@ -286,7 +286,7 @@ pub mod builtin {
     /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
     /// # }
     /// ```
-    #[unstable(feature = "concat_idents", issue = "29599")]
+    #[unstable(feature = "concat_idents_macro", issue = "29599")]
     #[macro_export]
     macro_rules! concat_idents {
         ($($e:ident),*) => ({ /* compiler built-in */ })