They are:
```
'S_BOARDRULES_LINK_ENABLED' => (!empty($this->config['boardrules_enable']) && !empty($this->config['boardrules_header_link'])) ? true : false,
```

S_BOARDRULES_ENABLED is effectively replaced by S_BOARDRULES_LINK_ENABLED, since the former had no function other than to act as a switch to display the link or not.