avoid "Undefined variable $unicode" warnings

[costing]

In the original form I was getting warnings like

<b>Warning</b>:  Undefined variable $unicode in <b>/var/www/html/admin/scripts/pi-hole/php/func.php</b> on line <b>687</b><br />

printed in the HTML output of /scripts/pi-hole/php/groups.php, which was not a valid JSON any more and led to an error displaying the blacklisted domains.

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[yubiuser]

Thanks for your PR. Please note, all PRs should be based on and target development branch.
The current code in development actually removed all PHP, so this change is not needed anymore.