Bad contract -> no contract. Unfortunately we've got a broken
6f1837723768f27a6f6a14452977e3e0e264f2cc contract on the mainnet which can't
be decoded (even though it had been saved successfully), so this is a
temporary fix for #2801 to be able to start mainnet node after shutdown.
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
This allows to reuse it across different packages.
testchain can't be used because of circular dependencies.
Init() is not changed except for filepath.Join() use instead of direct string
appends which is a better approach anyway. rootpath is required because
current directory will change from package to package.
