Don't emit missing_doc_code_examples on impl items

Author: GuillaumeGomez

src/librustdoc/passes/check_doc_test_visibility.rs

@@ -79,8 +79,7 @@ pub(crate) fn should_have_doc_example(cx: &DocContext<'_>, item: &clean::Item) -
                 | clean::ProvidedAssocConstItem(..)
                 | clean::ImplAssocConstItem(..)
                 | clean::RequiredAssocTypeItem(..)
-                // check for trait impl
-                | clean::ImplItem(box clean::Impl { trait_: Some(_), .. })
+                | clean::ImplItem(_)
         )
     {
         return false;