PushClient: migrate to ClearPersistentList DBus call
Newer version of lomiri-push-service are no longer able to understand "variadic argument" technique used previously, so now ClearPersistent can accept only 1 tag per call.
Switch to new ClearPersistentList which accepts an array of tags instead. This requires updated version of lomiri-push-service; since we're a system component we can effort this.