Terminal: Don't set an initial command_to_execute

Otherwise we end up executing "/bin/Shell -c /bin/Shell" on a normal
launch.  With a null command_to_execute, we'll just execute
/bin/Shell

Applications/Terminal/main.cpp

@@ -195,7 +195,7 @@ int main(int argc, char** argv)
  return 1;
  }
 
- const char* command_to_execute = "/bin/Shell";
+ const char* command_to_execute = nullptr;
 
  Core::ArgsParser args_parser;
  args_parser.add_option(command_to_execute, "Execute this command inside the terminal", nullptr, 'e', "command");