Remove useless feature attribute

mcarton · mcarton · commit 3bd0acaa5c75 · 2016-07-06T14:51:20.000+02:00
`iter_arith` has been stabilized in rustc 1.11.0.
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
@@ -3,7 +3,6 @@
 #![feature(box_syntax)]
 #![feature(collections)]
 #![feature(custom_attribute)]
-#![feature(iter_arith)]
 #![feature(question_mark)]
 #![feature(rustc_private)]
 #![feature(slice_patterns)]
