message: Fix compiler warning on uint64_t to int comparison
  nRollBackHeight was recently changed to an int which makes
  the casting of chainActive.Height() to a uint64_t unnnecessary.
diff: @@ -1111,7 +1111,7 @@ UniValue rollbackchain(const UniValue &params, bool fHelp)
  " blocks, however the limit is " + std::to_string(nLimit) + " blocks. Set " +
  "the override to true if you want rollback more than the default");
  - while ((uint64_t)chainActive.Height() > nRollBackHeight)
  + while (chainActive.Height() > nRollBackHeight)
  {
  // save the current tip
  CBlockIndex *pindex = chainActive.Tip();
  