use unset in your array before return or create a new array
unset($threads['per_page'] );
unset($threads['current_page'] );
unset($threads['prev_page_url'] );
unset($threads['from'] );
unset($threads['to'] );
return API::response()->array($threads);
or
$array = [
'next_page_url' => $threads['next_page_url'],
'data' => $threads['data']
]
return API::response()->array($array);
:)