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_bindings/android/os/IUpdateEngine.aidl b/binder_bindings/android/os/IUpdateEngine.aidl
index 8a5ec71..bbb86a3 100644
--- a/binder_bindings/android/os/IUpdateEngine.aidl
+++ b/binder_bindings/android/os/IUpdateEngine.aidl
@@ -58,4 +58,12 @@
    */
   long allocateSpaceForPayload(in String metadataFilename,
                                in String[] headerKeyValuePairs);
+  /** @hide
+   *
+   * Wait for merge to finish, and clean up necessary files.
+   *
+   * @return SUCCESS if successful. ERROR if transient errors (e.g. merged but
+   * needs reboot). DEVICE_CORRUPTED for permanent errors.
+   */
+  int cleanupSuccessfulUpdate();
 }