Don't require transitive dependencies in package set JSON

[paf31]

There's not really a need for this, we just need to have psc-package do the traversal to find all transitive dependencies. It should make it simpler to add a package to the set.

[seagreen]

I think this is really smart. Tracking derivable and original information separately is almost always a good move.

[paf31]

Working on it now 😄