[pkg] Use the new deprecated_system_package alias

PKG-46

Change-Id: Ie873faaf13309b536839ae5f75241f859dcf1e60
diff --git a/BUILD.gn b/BUILD.gn
index b6558f7..0e4895c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -123,7 +123,7 @@
 }
 
 package("vim") {
-  system_image = true
+  deprecated_system_image = true
 
   deps = [
     ":vim_bin",