API Lint: Ignore CallbackInterface in platform

It is okay to use callback interfaces because with Java 8 default interface
methods avoid the extensibility issue interfaces had previously.

Test: make checkapi
Change-Id: I7c931af638b83b4242f03dde9bc460b0981f66cd
diff --git a/Android.bp b/Android.bp
index 90dca03..d3b2c87 100644
--- a/Android.bp
+++ b/Android.bp
@@ -919,6 +919,7 @@
     "--hide-package com.android.org.conscrypt --hide-package com.android.server " +
     "--error UnhiddenSystemApi " +
     "--hide RequiresPermission " +
+    "--hide CallbackInterface " +
     "--hide MissingPermission --hide BroadcastBehavior " +
     "--hide HiddenSuperclass --hide DeprecationMismatch --hide UnavailableSymbol " +
     "--hide SdkConstant --hide HiddenTypeParameter --hide Todo --hide Typo "