Option was introduced back in c632dfb9
/ 5e500cdc to skip packages referenced
in dla-needed.txt, but never worked as intended: by default the script
already filters through unconditional 'pkg not in tracker.dla_needed'
tests, ever since the first revision, and was updated accordingly ever
since.

Dropping this option which causes confusion.

In the future, we might implement an option to skip dla-needed.txt
*itself*, as sometimes it's less confusing when all packages (triaged
or not) are displayed, though this can already be done simply by
temporarily truncating dla-needed.txt