Restore app_domain macro and move to private use.

app_domain was split up in commit: 2e00e6373faa6271d7839d33c5b9e69d998ff020 to
enable compilation by hiding type_transition rules from public policy.  These
rules need to be hidden from public policy because they describe how objects are
labeled, of which non-platform should be unaware.  Instead of cutting apart the
app_domain macro, which non-platform policy may rely on for implementing new app
types, move all app_domain calls to private policy.

(cherry-pick of commit: 76035ea01971156895cf0d8efc1876bfa2025bd6)

Bug: 33428593
Test: bullhead and sailfish both boot. sediff shows no policy change.
Change-Id: I4beead8ccc9b6e13c6348da98bb575756f539665
diff --git a/private/su.te b/private/su.te
index 3dda00f..b594ebe 100644
--- a/private/su.te
+++ b/private/su.te
@@ -11,8 +11,5 @@
 # su is also permissive to permit setenforce.
   permissive su;
 
-  # app_domain fallout
-  tmpfs_domain(su)
-  # Map with PROT_EXEC.
-  allow su su_tmpfs:file execute;
+  app_domain(su)
 ')