Set updatable=false explicitly.

Currently, this is the default so this is a no-op,
But the default is changing to true.

Bug: 180375550
Test: Treehugger
Change-Id: I74cfd805958687a4c1e43eded31fb0e6583c1482
diff --git a/apex/Android.bp b/apex/Android.bp
index 16422f8..19894f1 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -51,6 +51,7 @@
     prebuilts: [
         "bionic-linker-config",
     ],
+    updatable: false,
 }
 
 sdk {