Add stubs for UpdateEngine.CleanupSuccessfulUpdate

This API waits for merge to finish after rebooting to
the new Virtual A/B build.

Test: pass
Bug: 138808328
Change-Id: I9422f0ffb1876b71ab45e994fc2d5c76d9ec3a75
diff --git a/binder_service_android.h b/binder_service_android.h
index 5207075..1c38d2b 100644
--- a/binder_service_android.h
+++ b/binder_service_android.h
@@ -74,6 +74,8 @@
       const android::String16& metadata_filename,
       const std::vector<android::String16>& header_kv_pairs,
       int64_t* return_value) override;
+  android::binder::Status cleanupSuccessfulUpdate(
+      int32_t* return_value) override;
 
  private:
   // Remove the passed |callback| from the list of registered callbacks. Called