Rename product_services to system_ext

Bug: 134359158
Test: build and check if system_ext.img is created
Change-Id: Ice3229baf97a94c24a6eea22e7d4571941d7f843
diff --git a/ui/build/cleanbuild.go b/ui/build/cleanbuild.go
index c47f614..8e7f96a 100644
--- a/ui/build/cleanbuild.go
+++ b/ui/build/cleanbuild.go
@@ -111,7 +111,7 @@
 		productOut("system_other"),
 		productOut("vendor"),
 		productOut("product"),
-		productOut("product_services"),
+		productOut("system_ext"),
 		productOut("oem"),
 		productOut("obj/FAKE"),
 		productOut("breakpad"),