[ticket/11863] Set require_activation to none if emails are disabled

https://tracker.phpbb.com/browse/PHPBB3-11863
There is no need for nested loops. How about this?
```php
    function select_acc_activation($selected_value, $value)
    {
        global $user, $config;

        $act_array = array(
            'ACC_DISABLE' => array(true, USER_ACTIVATION_DISABLE),
            'ACC_NONE'    => array(true, USER_ACTIVATION_NONE),
            'ACC_USER'    => array($config['email_enable'], USER_ACTIVATION_SELF),
            'ACC_ADMIN'   => array($config['email_enable'], USER_ACTIVATION_ADMIN),
        );

        $act_options = '';

        foreach ($act_array as $data)
        {
            list($available, $value) = $data;
            $selected = ($selected_value == $value) ? ' selected="selected"' : '';
            $class = ($available) ? ' class="disabled-option"' : '';
            $act_options .= '<option value="' . $value . '"' . $selected . $class '>' . $user->lang($key) . '</option>';
        }

        return $act_options;
    }
```
Even better would be passing this to the template engine.