message: [json-rpc] fix unused_imports
diff: @@ -10,7 +10,7 @@ use jsonrpc_core::IoHandler;
  use starcoin_logger::prelude::*;
  use std::cell::RefCell;
  use std::sync::Arc;
  -use traits::{mock::MockTxPoolService, TxPoolAsyncService};
  +use traits::TxPoolAsyncService;
  mod module;
  mod server;
  @@ -74,6 +74,7 @@ impl Supervised for JSONRpcActor {
  #[cfg(test)]
  mod tests {
  use super::*;
  + use traits::mock::MockTxPoolService;
  #[stest::test]
  async fn test_start() {
  