message: Remove unused variable in unlimited.cpp
  Spotted by clang, this is the fixed warning:
  unlimited.cpp:2229:36: warning: unused variable 'n' [-Wunused-variable]
  std::vector<CNode *>::iterator n;
diff: @@ -2226,7 +2226,6 @@ extern UniValue getstructuresizes(const UniValue &params, bool fHelp)
  #endif
  LOCK(cs_vNodes);
  - std::vector<CNode *>::iterator n;
  int disconnected = 0; // watch # of disconnected nodes to ensure they are being cleaned up
  for (std::vector<CNode *>::iterator it = vNodes.begin(); it != vNodes.end(); ++it)
  {
  