One service needed session_id in its license call, which a near-duplicate of get_content_keys supplied behind a service-tag test. service_licence now passes each service only the arguments its own license function declares, so the duplicate and the branch are gone. The REST API license paths and the base PlayReady delegate get the same filtering, replacing their fixed argument set.
Two behaviour changes ride along: an empty license challenge now raises EmptyLicense for every service, not just the one, and a service that declares only challenge now receives a working call instead of a TypeError.
