scrub-obsolete should update any build-dependencies, test-dependencies or other
dependencies on either:

 * packages that are transitional and for which the replacement can be derived
 * packages that have been removed but were present in the past and
   that have a single current package that Provides: them

hi,

actually there's already a bug, #982655 (cc:ed), titled "scrub-obsolete: replace
dependencies on transitional or removed packages" which I believed could be extended
to also cover removing transitional packages which have been present for more than
2 releases.

Jelmer, do you agree or do you want another bug for this feature request?