message: Do not show already spent mints in exodus_listmints
diff: @@ -1919,7 +1919,7 @@ UniValue exodus_listmints(const UniValue& params, bool fHelp)
  std::vector<SigmaMint> mints;
  wallet->ListSigmaMints(boost::make_function_output_iterator([&] (const SigmaMint& m) {
  - if (m.chainState.block < 0) {
  + if (!m.spentTx.IsNull() || m.chainState.block < 0) {
  return;
  }
  