Remove unused Debian services and worker

Following https://docs.gitlab.com/ee/development/sidekiq/compatibility_across_updates.html#removing-worker-classes

One release after ::Packages::Debian::ProcessChanges{Worker,Service} are no longer used (i.e %16.2 as !115776 (merged) was merged in %16.1).

Part 2/2 of #399197 (closed)