Limit ravenwood related module visibilities

... to prevent other people from using them.

Test: ./scripts/run-all-tests.sh
Bug: 292141694
Change-Id: Ia45edead270883116446e8db6abde080d341ab07
diff --git a/Ravenwood.bp b/Ravenwood.bp
index 9218cc9..da02298 100644
--- a/Ravenwood.bp
+++ b/Ravenwood.bp
@@ -59,6 +59,7 @@
 // Extract the impl jar from "framework-minus-apex.ravenwood-base" for subsequent build rules.
 java_genrule_host {
     name: "framework-minus-apex.ravenwood",
+    defaults: ["hoststubgen-for-prototype-only-genrule"],
     cmd: "cp $(in) $(out)",
     srcs: [
         ":framework-minus-apex.ravenwood-base{ravenwood.jar}",
@@ -66,5 +67,4 @@
     out: [
         "framework-minus-apex.ravenwood.jar",
     ],
-    visibility: ["//visibility:public"],
 }