remove unused code (#1920)

substrate/srml/system/src/lib.rs

@@ -193,7 +193,9 @@ impl From<RawLog<substrate_primitives::H256>> for primitives::testing::DigestIte
 	}
 }
 
-// Create a Hash with 69 for each byte
+// Create a Hash with 69 for each byte,
+// only used to build genesis config
+#[cfg(feature = "std")]
 fn hash69<T: AsMut<[u8]> + Default>() -> T {
 	let mut h = T::default();
 	h.as_mut().iter_mut().for_each(|byte| *byte = 69);