code refactor

Author: chenyukang

tx-pool/src/component/orphan.rs

@@ -154,10 +154,10 @@ impl OrphanPool {
         self.limit_size()
     }
 
-    pub fn find_by_previous(&self, tx: &TransactionView) -> Vec<ProposalShortId> {
+    pub fn find_by_previous(&self, tx: &TransactionView) -> Vec<&ProposalShortId> {
         tx.output_pts()
             .iter()
-            .filter_map(|out_point| self.by_out_point.get(out_point).cloned())
+            .filter_map(|out_point| self.by_out_point.get(out_point))
             .flatten()
             .collect::<Vec<_>>()
     }