libhwminijail: visibility hidden

Avoid dependencies on this until existing users can be clean up.
Unfortunately, we can only guard this in Soong, where there are no users
at this current time.

Bug: 110363419
Test: build only (only build checks are added)
Change-Id: If25e8a6c35a0e1edcdd821371287e801577a9540
diff --git a/minijail/Android.bp b/minijail/Android.bp
index c01a12b..e025033 100644
--- a/minijail/Android.bp
+++ b/minijail/Android.bp
@@ -1,3 +1,6 @@
+// TODO(b/110363419): remove or make failures harder
+// Deprecated: most minijail users should either use libavservices_minijail
+// or reinstitute this (w/ fatal checks).
 cc_library_shared {
     name: "libhwminijail",
     defaults: ["hidl_defaults"],
@@ -10,4 +13,5 @@
         "libbase",
         "libminijail",
     ],
+    visibility: [":__subpackages__"],
 }