Do not clone pending changes

Discarding prospective changes should be equivalent as a state machine
is not to be called with peding changes.

This will be replaced by a storage transaction that is rolled back before
executing the call the second time removing this constraint.

primitives/state-machine/src/lib.rs

@@ -345,11 +345,10 @@ impl<'a, B, H, N, Exec> StateMachine<'a, B, H, N, Exec> where
 				CallResult<R, Exec::Error>,
 			) -> CallResult<R, Exec::Error>
 	{
-		let pending_changes = self.overlay.clone_pending();
 		let (result, was_native) = self.execute_aux(true, native_call.take());
 
 		if was_native {
-			self.overlay.set_pending(pending_changes);
+			self.overlay.discard_prospective();
 			let (wasm_result, _) = self.execute_aux(
 				false,
 				native_call,
@@ -376,7 +375,6 @@ impl<'a, B, H, N, Exec> StateMachine<'a, B, H, N, Exec> where
 			R: Decode + Encode + PartialEq,
 			NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
 	{
-		let pending_changes = self.overlay.clone_pending();
 		let (result, was_native) = self.execute_aux(
 			true,
 			native_call.take(),
@@ -385,7 +383,7 @@ impl<'a, B, H, N, Exec> StateMachine<'a, B, H, N, Exec> where
 		if !was_native || result.is_ok() {
 			result
 		} else {
-			self.overlay.set_pending(pending_changes);
+			self.overlay.discard_prospective();
 			let (wasm_result, _) = self.execute_aux(
 				false,
 				native_call,

primitives/state-machine/src/overlayed_changes.rs

@@ -535,16 +535,6 @@ impl OverlayedChanges {
 		committed.into_iter().flatten().chain(prospective.into_iter().flatten())
 	}
 
-	/// Return a clone of the currently pending changes.
-	pub fn clone_pending(&self) -> OverlayedChangeSet {
-		self.prospective.clone()
-	}
-
-	/// Replace the currently pending changes.
-	pub fn set_pending(&mut self, pending: OverlayedChangeSet) {
-		self.prospective = pending;
-	}
-
 	/// Convert this instance with all changes into a [`StorageChanges`] instance.
 	pub fn into_storage_changes<
 		B: Backend<H>, H: Hasher, N: BlockNumber