Use blueprint/pool

Use blueprint's typesafe sync.Pool.

Test: builds
Change-Id: I3de1c455f229eb23ac3ca3dc0baa3bdd7bc0d5d6
diff --git a/android/transition.go b/android/transition.go
index e1aa891..0677ca1 100644
--- a/android/transition.go
+++ b/android/transition.go
@@ -197,7 +197,7 @@
 func (a *androidTransitionMutatorAdapter) OutgoingTransition(bpctx blueprint.OutgoingTransitionContext,
 	sourceTransitionInfo blueprint.TransitionInfo) blueprint.TransitionInfo {
 	m := bpctx.Module().(Module)
-	ctx := outgoingTransitionContextPool.Get().(*outgoingTransitionContextImpl)
+	ctx := outgoingTransitionContextPool.Get()
 	defer outgoingTransitionContextPool.Put(ctx)
 	*ctx = outgoingTransitionContextImpl{
 		archModuleContext: m.base().archModuleContextFactory(bpctx),
@@ -209,7 +209,7 @@
 func (a *androidTransitionMutatorAdapter) IncomingTransition(bpctx blueprint.IncomingTransitionContext,
 	incomingTransitionInfo blueprint.TransitionInfo) blueprint.TransitionInfo {
 	m := bpctx.Module().(Module)
-	ctx := incomingTransitionContextPool.Get().(*incomingTransitionContextImpl)
+	ctx := incomingTransitionContextPool.Get()
 	defer incomingTransitionContextPool.Put(ctx)
 	*ctx = incomingTransitionContextImpl{
 		archModuleContext: m.base().archModuleContextFactory(bpctx),