tests: remove data-dir argument registration

It is already registered in cryptonote::core::init_options,
which we now call

tests/core_tests/chaingen.h

@@ -474,7 +474,6 @@ inline bool do_replay_events(std::vector<test_event_entry>& events)
 {
   boost::program_options::options_description desc("Allowed options");
   cryptonote::core::init_options(desc);
-  command_line::add_arg(desc, command_line::arg_data_dir);
   boost::program_options::variables_map vm;
   bool r = command_line::handle_error_helper(desc, [&]()
   {