Convert orderfile mutators to TransitionMutator

Convert orderfileDepsMutator and orderfileMutator to a TransitionMutator
as a step towards variants-on-demand.

Bug: 319288033
Test: orderfile_test.go

Change-Id: I27df65b7264a5b059a900e7ea04c18dfb2787a84
diff --git a/cc/cc.go b/cc/cc.go
index 31fa4fd..1a9c7bf 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -73,8 +73,7 @@
 		ctx.TopDown("afdo_deps", afdoDepsMutator)
 		ctx.BottomUp("afdo", afdoMutator).Parallel()
 
-		ctx.TopDown("orderfile_deps", orderfileDepsMutator)
-		ctx.BottomUp("orderfile", orderfileMutator).Parallel()
+		ctx.Transition("orderfile", &orderfileTransitionMutator{})
 
 		ctx.Transition("lto", &ltoTransitionMutator{})