Bug#554006: lintian: Warn if package ships files in /etc/cron.* without depending on cron

[Josh Triplett <josh@joshtriplett.org>]

I don't think lintian should warn about this, for two reasons:

- It's possible to have an *optional* cron script, not required for
  package functionality, which might warrant at most a `Suggests`.
- If a script ships both a cron script and a systemd .timer file, it
  need not depend on cron.