use substore prefix in delete

crates/bin/pd/src/migrate/testnet78.rs

@@ -179,7 +179,7 @@ async fn delete_empty_deleted_packet_commitments(
     pin_mut!(stream_empty_commitments);
 
     while let Some(key) = stream_empty_commitments.next().await {
-        delta.delete(key);
+        delta.delete(format!("ibc-data/{}", key));
     }
 
     Ok(())