Remove very useless as_substs usage from clippy

Author: WaffleLapkin

src/tools/clippy/clippy_utils/src/ty.rs

@@ -975,7 +975,7 @@ pub fn approx_ty_size<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> u64 {
     }
     match (cx.layout_of(ty).map(|layout| layout.size.bytes()), ty.kind()) {
         (Ok(size), _) => size,
-        (Err(_), ty::Tuple(list)) => list.as_substs().types().map(|t| approx_ty_size(cx, t)).sum(),
+        (Err(_), ty::Tuple(list)) => list.iter().map(|t| approx_ty_size(cx, t)).sum(),
         (Err(_), ty::Array(t, n)) => {
             n.try_eval_target_usize(cx.tcx, cx.param_env).unwrap_or_default() * approx_ty_size(cx, *t)
         },