Refactor distributor API so that methods always get the Quest_Desc too.

dm/appengine/mutate/schedule_execution.go

Index: dm/appengine/mutate/schedule_execution.go
diff --git a/dm/appengine/mutate/schedule_execution.go b/dm/appengine/mutate/schedule_execution.go
index f65a166a9a206523867841e160f0b0b707721bf8..09fc6d0686c28f7151bf5da2f45a04ecfdaa84a1 100644
--- a/dm/appengine/mutate/schedule_execution.go
+++ b/dm/appengine/mutate/schedule_execution.go
@@ -80,8 +80,7 @@ func (s *ScheduleExecution) RollForward(c context.Context) (muts []tumble.Mutati
 	exAuth := &dm.Execution_Auth{Id: eid, Token: e.Token}
 
 	var distTok distributor.Token
-	distTok, e.TimeToStop, err = dist.Run(
-		distributor.NewTaskDescription(c, &q.Desc, exAuth, prevResult))
+	distTok, e.TimeToStop, err = dist.Run(&q.Desc, exAuth, prevResult)
 	if e.TimeToStop <= 0 {
 		e.TimeToStop = q.Desc.Meta.Timeouts.Stop.Duration()
 	}