Exclude d-i packages (udeb packages) from l10n material

gen-material: Exclude d-i packages (udeb packages) from central l10n statistics infrastructure (currently found under https://www.debian.org/international/l10n/po-debconf/). d-i manages its translations via the l10n-sync script, which makes it not useful for translators, to work on those packages as stand-alone packages (causes extra work for d-i l10n coordinator). d-i has its own l10n infrastructure and statistics.