message: [RPC] Remove warning for removed estimatefee RPC
  The  RPC was removed in a previous version, but a warning was
  left for users to use the estimatesmartfee RPC. Remove that warning now
  that estimatefee has been gone for over one version.
diff: @@ -795,12 +795,6 @@ static UniValue submitheader(const JSONRPCRequest& request)
  throw JSONRPCError(RPC_VERIFY_ERROR, state.GetRejectReason());
  }
  -static UniValue estimatefee(const JSONRPCRequest& request)
  -{
  - throw JSONRPCError(RPC_METHOD_DEPRECATED, "estimatefee was removed in v0.17.\n"
  - "Clients should use estimatesmartfee.");
  -}
  -
  static UniValue estimatesmartfee(const JSONRPCRequest& request)
  {
  if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
  @@ -978,7 +972,6 @@ static const CRPCCommand commands[] =
  { "generating", "generatetoaddress", &generatetoaddress, {"nblocks","address","maxtries"} },
  - { "hidden", "estimatefee", &estimatefee, {} },
  { "util", "estimatesmartfee", &estimatesmartfee, {"conf_target", "estimate_mode"} },
  { "hidden", "estimaterawfee", &estimaterawfee, {"conf_target", "threshold"} },
  