remove-reprepro-codename: run reprepro's clearvanished with --delete option

There might be packages left in the repos:

| # reprepro -b /srv/repository/ clearvanished
| There are still packages in 'foo/bar|main|amd64', not removing (give --delete to do so)!
| There are still packages in 'foo/bar|main|i386', not removing (give --delete to do so)!
| There are still packages in 'foo/bar|main|source', not removing (give --delete to do so)!

So get rid of the repos, no matter what.