nit: use format! instead of iterator

src/librustc/hir/svh.rs

@@ -36,17 +36,7 @@ impl Svh {
     }
 
     pub fn to_string(&self) -> String {
-        let hash = self.hash;
-        return (0..64).step_by(4).map(|i| hex(hash >> i)).collect();
-
-        fn hex(b: u64) -> char {
-            let b = (b & 0xf) as u8;
-            let b = match b {
-                0 ... 9 => '0' as u8 + b,
-                _ => 'a' as u8 + b - 10,
-            };
-            b as char
-        }
+        format!("{:016x}", self.hash)
     }
 }
 

src/librustc/lib.rs

@@ -37,7 +37,6 @@
 #![feature(rustc_private)]
 #![feature(slice_patterns)]
 #![feature(staged_api)]
-#![feature(step_by)]
 #![feature(question_mark)]
 #![cfg_attr(test, feature(test))]