It apparently broke clean builds, as the dependencies aren't in the project asset list or something anymore. I tried to fix this, but it seems impossible to do without relying on .NET SDK internals, as there's no point in the NuGet graph walk process that seems cleanly extensible.
Instead let's just do the much dumber thing: a bunch of .props files for content to import. Hooray!
This also means that I have to go through and *explicitly* disable transitive dependencies everywhere in RT. This thankfully isn't too hard.
