Remove unneeded #[lang = "iterator"]

Author: GuillaumeGomez

src/libcore/iter.rs

@@ -321,7 +321,6 @@ fn _assert_is_object_safe(_: &Iterator<Item=()>) {}
 ///
 /// [module-level documentation]: index.html
 /// [impl]: index.html#implementing-iterator
-#[lang = "iterator"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented = "`{Self}` is not an iterator; maybe try calling \
                             `.iter()` or a similar method"]