psbt_wallet_tests: use unique_ptr for GetSigningProvider
psbt_wallet_tests: use unique_ptr for GetSigningProvider


Former-commit-id: 0041924ed5118583f5a4180cf19f7fb6b6fbce49
syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2