Rollup merge of #110864 - compiler-errors:into-future-stable, r=jackh726

`IntoFuture::into_future` is no longer unstable

We don't need to gate the `IntoFuture::into_future` call in `.await` lowering anymore.

``@bors`` rollup

compiler/rustc_ast_lowering/src/expr.rs

@@ -858,13 +858,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let awaitee_arm = self.arm(awaitee_pat, loop_expr);
 
         // `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
-        let into_future_span = self.mark_span_with_reason(
-            DesugaringKind::Await,
-            dot_await_span,
-            self.allow_into_future.clone(),
-        );
         let into_future_expr = self.expr_call_lang_item_fn(
-            into_future_span,
+            span,
             hir::LangItem::IntoFutureIntoFuture,
             arena_vec![self; expr],
             Some(expr_hir_id),

compiler/rustc_ast_lowering/src/item.rs

@@ -83,7 +83,6 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             impl_trait_bounds: Vec::new(),
             allow_try_trait: Some([sym::try_trait_v2, sym::yeet_desugar_details][..].into()),
             allow_gen_future: Some([sym::gen_future, sym::closure_track_caller][..].into()),
-            allow_into_future: Some([sym::into_future][..].into()),
             generics_def_id_map: Default::default(),
         };
         lctx.with_hir_id_owner(owner, |lctx| f(lctx));

compiler/rustc_ast_lowering/src/lib.rs

@@ -136,7 +136,6 @@ struct LoweringContext<'a, 'hir> {
 
     allow_try_trait: Option<Lrc<[Symbol]>>,
     allow_gen_future: Option<Lrc<[Symbol]>>,
-    allow_into_future: Option<Lrc<[Symbol]>>,
 
     /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
     /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic