optimize TypeFoldable for 2 element tuples

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -889,19 +889,6 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ty::Binder<'tcx, ty::Existentia
     }
 }
 
-impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
-    fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.intern_type_list(v))
-    }
-
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
-        self.iter().try_for_each(|t| t.visit_with(visitor))
-    }
-}
-
 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ProjectionKind> {
     fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
         self,