i18n: Plural does not work with two variables

[rakekniven]

https://github.com/nextcloud/contacts/blob/cf7cbece3a35ebbec1ffc254db23d67e08b3baec/lib/Controller/ImportController.php#L180-L185

Both of these numbers can take a different plural form, so this is wrong formulation. (skipped %d) should be in a separate source string.