Simplify ClearNoteWitnessCache()

src/wallet/wallet.cpp

@@ -597,8 +597,7 @@ void CWallet::ClearNoteWitnessCache()
     LOCK(cs_wallet);
     for (std::pair<const uint256, CWalletTx>& wtxItem : mapWallet) {
         for (mapNoteData_t::value_type& item : wtxItem.second.mapNoteData) {
-            CNoteData* nd = &(item.second);
-            nd->witnesses.clear();
+            item.second.witnesses.clear();
         }
     }
 }