message: Fix irrelevant receipt status message
  Since security level has been removed, this status message needed to be
  changed.
  Also removed some stale unused code that was left over from when
  security level was used.
diff: @@ -4744,7 +4744,7 @@ bool CWallet::MintsToInputVector(std::map<CBigNum, CZerocoinMint>& mapMintsSelec
  // Generate the witness for each mint being spent
  if (!GenerateAccumulatorWitness(coinWitness, mapAccumulators, pindexCheckpoint)) {
  - receipt.SetStatus(_("Try to spend with a higher security level to include more coins"),
  + receipt.SetStatus(_("Couldn't generate the accumulator witness"),
  ZPIV_FAILED_ACCUMULATOR_INITIALIZATION);
  return error("%s : %s", __func__, receipt.GetStatusMessage());
  }
  @@ -5003,13 +5003,6 @@ bool CWallet::CreateZerocoinSpendTransaction(CAmount nValue, CWalletTx& wtxNew,
  //hash with only the output info in it to be used in Signature of Knowledge
  uint256 hashTxOut = txNew.GetHash();
  - //Use the same accumulator checkpoint for each spend
  - int nHeightHighest = 0;
  - for (const CZerocoinMint& mint : vSelectedMints) {
  - if (mint.GetHeight() > nHeightHighest)
  - nHeightHighest = mint.GetHeight();
  - }
  -
  CBlockIndex* pindexCheckpoint = nullptr;
  std::map<CBigNum, CZerocoinMint> mapSelectedMints;
  for (const CZerocoinMint& mint : vSelectedMints)
  