{Input,Output}EffectiveStatement should be DataTreeEffectiveStatement

Both RpcEffectiveStatement and ActionEffectiveStatement are DataTreeAwareEffeciveStatements, implying they are indexing their children into data tree. They can contain only {Input,Output}EffectiveStatement, which are not DataTreeEffectiveStatements – hence the data tree view ends up being empty after fixing YANGTOOLS-1292.