Rollup merge of #127630 - compiler-errors:type-ascription, r=chenyukang

Remove lang feature for type ascription (since it's a lib feature now)

It's not necessary since it's a library feature now, via the type ascription macro. We can't (and shouldn't) register it as a removed feature since I think that would give "this feature has been removed" errors even for people using the macro (well, I'm pretty sure, though I didn't check).

r? `@Nilstrieb`

compiler/rustc_codegen_gcc/example/mini_core.rs

@@ -1,5 +1,5 @@
 #![feature(
-    no_core, lang_items, intrinsics, unboxed_closures, type_ascription, extern_types,
+    no_core, lang_items, intrinsics, unboxed_closures, extern_types,
     decl_macro, rustc_attrs, transparent_unions, auto_traits, freeze_impls,
     thread_local
 )]

compiler/rustc_feature/src/unstable.rs

@@ -621,8 +621,6 @@ declare_features! (
     (unstable, try_blocks, "1.29.0", Some(31436)),
     /// Allows `impl Trait` to be used inside type aliases (RFC 2515).
     (unstable, type_alias_impl_trait, "1.38.0", Some(63063)),
-    /// Allows the use of type ascription in expressions.
-    (unstable, type_ascription, "1.6.0", Some(23416)),
     /// Allows creation of instances of a struct by moving fields that have
     /// not changed from prior instances of the same struct (RFC #2528)
     (unstable, type_changing_struct_update, "1.58.0", Some(86555)),