Decide on cosmetic rkhunter cron.daily/weekly cleanup + apt-daily mask follow-through

Two small leftover items from the 2026-08-26 pass: (1) optionally purge inert /etc/cron.daily/rkhunter + /etc/cron.weekly/rkhunter (already no-op via /etc/default/rkhunter, cosmetic only). (2) apt-daily.timer/apt-daily-upgrade.timer are now masked - confirm no downstream assumption anywhere relies on them (e.g. any script checking apt cache freshness).