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/libcore/cmp.rs

@@ -706,24 +706,24 @@ mod impls {
 
     ord_impl! { char usize u8 u16 u32 u64 isize i8 i16 i32 i64 }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[unstable(feature = "never_type_impls", issue = "35121")]
     impl PartialEq for ! {
         fn eq(&self, _: &!) -> bool {
             *self
         }
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[unstable(feature = "never_type_impls", issue = "35121")]
     impl Eq for ! {}
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[unstable(feature = "never_type_impls", issue = "35121")]
     impl PartialOrd for ! {
         fn partial_cmp(&self, _: &!) -> Option<Ordering> {
             *self
         }
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[unstable(feature = "never_type_impls", issue = "35121")]
     impl Ord for ! {
         fn cmp(&self, _: &!) -> Ordering {
             *self