Revert "Revert "Change apex_available value of libavf based on a..."

Revert submission 3481353-revert-3477737-move_apex_shortcut-EGRJFKGUNB

Reason for revert: relanding with fix

Reverted changes: /q/submissionid:3481353-revert-3477737-move_apex_shortcut-EGRJFKGUNB

Change-Id: Ib1d21c4db0ba652c59450ca2fa0743158e299d49
diff --git a/guest/authfs/Android.bp b/guest/authfs/Android.bp
index d7a8322..28e0f4a 100644
--- a/guest/authfs/Android.bp
+++ b/guest/authfs/Android.bp
@@ -47,5 +47,8 @@
 rust_binary {
     name: "authfs",
     defaults: ["authfs_defaults"],
-    apex_available: ["com.android.virt"],
+    // //apex_available:platform is necessary here to counteract the
+    // com.android.virt in crosvm_defaults and make authfs available
+    // to the platform so it can be embedded in the microdroid image.
+    apex_available: ["//apex_available:platform"],
 }