Replace type_alias_impl_trait by min_type_alias_impl_trait with no actual changes in behaviour

This makes `type_alias_impl_trait` not actually do anything anymore

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -279,7 +279,7 @@ impl<'a> PostExpansionVisitor<'a> {
                 if let ast::TyKind::ImplTrait(..) = ty.kind {
                     gate_feature_post!(
                         &self.vis,
-                        type_alias_impl_trait,
+                        min_type_alias_impl_trait,
                         ty.span,
                         "`impl Trait` in type aliases is unstable"
                     );