Stabilize RFC3324 dyn upcasting coercion

Aka trait_upcasting feature.

And also adjust the `deref_into_dyn_supertrait` lint.

compiler/rustc_lint/src/deref_into_dyn_supertrait.rs

@@ -5,7 +5,6 @@ use crate::{
 
 use rustc_hir as hir;
 use rustc_middle::ty;
-use rustc_session::lint::FutureIncompatibilityReason;
 use rustc_span::sym;
 use rustc_trait_selection::traits::supertraits;
 
@@ -13,9 +12,6 @@ declare_lint! {
     /// The `deref_into_dyn_supertrait` lint is output whenever there is a use of the
     /// `Deref` implementation with a `dyn SuperTrait` type as `Output`.
     ///
-    /// These implementations will become shadowed when the `trait_upcasting` feature is stabilized.
-    /// The `deref` functions will no longer be called implicitly, so there might be behavior change.
-    ///
     /// ### Example
     ///
     /// ```rust,compile_fail
@@ -44,15 +40,10 @@ declare_lint! {
     ///
     /// ### Explanation
     ///
-    /// The dyn upcasting coercion feature adds new coercion rules, taking priority
-    /// over certain other coercion rules, which will cause some behavior change.
+    /// The implicit dyn upcasting coercion take priority over those `Deref` impls.
     pub DEREF_INTO_DYN_SUPERTRAIT,
     Warn,
-    "`Deref` implementation usage with a supertrait trait object for output might be shadowed in the future",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
-        reference: "issue #89460 <https://github.com/rust-lang/rust/issues/89460>",
-    };
+    "`Deref` implementation usage with a supertrait trait object for output are shadow by implicit coercion",
 }
 
 declare_lint_pass!(DerefIntoDynSupertrait => [DEREF_INTO_DYN_SUPERTRAIT]);
@@ -90,7 +81,7 @@ impl<'tcx> LateLintPass<'tcx> for DerefIntoDynSupertrait {
             cx.emit_spanned_lint(
                 DEREF_INTO_DYN_SUPERTRAIT,
                 tcx.def_span(item.owner_id.def_id),
-                SupertraitAsDerefTarget { t, target_principal, label },
+                SupertraitAsDerefTarget { t, label },
             );
         }
     }