IUpdateEngine.cleanupSuccessfulUpdate is async

UpdateAttempterAndroid::CleanupSuccessfulUpdate uses
CleanupPreviousUpdateAction, which is asynchronous. Hence,
the binder function needs to be asynchronous too.

Test: update_attempter_android --merge after update
Bug: 147696014

Change-Id: I0ce43db6d75a5a13a105c25645824612bd4d6be3
diff --git a/common/action.h b/common/action.h
index c93e73c..fd82c2d 100644
--- a/common/action.h
+++ b/common/action.h
@@ -229,7 +229,8 @@
   void PerformAction() override {
     processor_->ActionComplete(this, ErrorCode::kSuccess);
   }
-  std::string Type() const override { return "NoOpAction"; }
+  static std::string StaticType() { return "NoOpAction"; }
+  std::string Type() const override { return StaticType(); }
 };
 
 };  // namespace chromeos_update_engine