It's Clippy time (#3806)

Fix some Clippy issues

substrate/srml/support/src/hash.rs

@@ -59,7 +59,7 @@ impl StorageHasher for Twox64Concat {
 	type Output = Vec<u8>;
 	fn hash(x: &[u8]) -> Vec<u8> {
 		twox_64(x)
-			.into_iter()
+			.iter()
 			.chain(x.into_iter())
 			.cloned()
 			.collect::<Vec<_>>()

substrate/srml/support/src/traits.rs

@@ -148,7 +148,7 @@ pub trait OnUnbalanced<Imbalance> {
 	fn on_unbalanced(amount: Imbalance);
 }
 
-impl<Imbalance: Drop> OnUnbalanced<Imbalance> for () {
+impl<Imbalance> OnUnbalanced<Imbalance> for () {
 	fn on_unbalanced(amount: Imbalance) { drop(amount); }
 }
 

substrate/srml/system/src/lib.rs

@@ -567,7 +567,7 @@ impl<T: Trait> Module<T> {
 		// We perform early return if we've reached the maximum capacity of the event list,
 		// so `Events<T>` seems to be corrupted. Also, this has happened after the start of execution
 		// (since the event list is cleared at the block initialization).
-		if <Events<T>>::append([event].into_iter()).is_err() {
+		if <Events<T>>::append([event].iter()).is_err() {
 			// The most sensible thing to do here is to just ignore this event and wait until the
 			// new block.
 			return;