Add and use generics.is_empty() and generics.is_own_empty, rather than using generics' attributes

Author: spastorino

clippy_lints/src/iter_without_into_iter.rs

@@ -225,7 +225,7 @@ impl {self_ty_without_ref} {{
             && let ImplItemKind::Fn(sig, _) = item.kind
             && let FnRetTy::Return(ret) = sig.decl.output
             && is_nameable_in_impl_trait(ret)
-            && cx.tcx.generics_of(item_did).own_params.is_empty()
+            && cx.tcx.generics_of(item_did).is_own_empty()
             && sig.decl.implicit_self == expected_implicit_self
             && sig.decl.inputs.len() == 1
             && let Some(imp) = get_parent_as_impl(cx.tcx, item.hir_id())

clippy_utils/src/ty/type_certainty/mod.rs

@@ -176,7 +176,7 @@ fn qpath_certainty(cx: &LateContext<'_>, qpath: &QPath<'_>, resolves_to_type: bo
             .get(*lang_item)
             .map_or(Certainty::Uncertain, |def_id| {
                 let generics = cx.tcx.generics_of(def_id);
-                if generics.parent_count == 0 && generics.own_params.is_empty() {
+                if generics.is_empty() {
                     Certainty::Certain(if resolves_to_type { Some(def_id) } else { None })
                 } else {
                     Certainty::Uncertain