refactor: Use Mutex type for g_cs_recent_confirmed_transactions
refactor: Use Mutex type for g_cs_recent_confirmed_transactions

Former-commit-id: accb4d09c4c11a8c00c0cd34aba9b40936dbc17a
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin