update_engine: Use only backuptool_postinstall on Weekly build

Change-Id: Ib8eb87fe58fbb6310c5f3e20b2136885f07df65c
diff --git a/Android.bp b/Android.bp
index be9f44c..92c993b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -291,6 +291,7 @@
         "ue_defaults",
         "libpayload_consumer_exports",
         "libpayload_consumer_defaults",
+        "omni_weekly_build_defaults",
     ],
 }
 
@@ -300,6 +301,7 @@
         "ue_defaults",
         "libpayload_consumer_exports_proto-full",
         "libpayload_consumer_defaults",
+        "omni_weekly_build_defaults",
     ],
 }