They were first introduced in a058598ecc and
then carefully moved in 648e0bb242, but it looks
like they were never used by any external code. This code can be useful on the
server, but the server has its own params package to deal with
parameters. Clients usually create Parameters and then get results as
stackitem.Items, so they don't use this code either. So there is zero point in
keeping it.
1. It's not good for pkg/core to import anything from pkg/neorpc.
2. The type is closely tied to the state package, even though it's not stored
in the DB
