There seems there is no way to get rid of it. Nothing I could find a way to uninstall it. In the Purchased tab, I found this app as Installed. Right click on it, I could hide it. But still the red 1 badge was still hanging there.
Today I finally find a way to vanish the badge 1. It is quite simple. I started with with the uninstallation. In Mac, to remove an app is very simple: find it and trash it.
I bring my SpotLight by pressing command + space key. Type "DropCopy". Then hold command key and click on it. The find is opened. To my surprise, the DropCopy is in the folder of "MyApplication" under Applications!
I moved "MyApplication" from root to "Applications". I had a reason to keep all the apps I found from web or none-Apple places within "MyApplication". That was good idea until I realized that I could not restore it back from TimeMachine back if I want only one account and applications restored. That's why I moved "MyApplication" to Applications. I think that I might have a sticky mouse to moved DropCopy to "MyApplication" without my notice. As a result, I think, it caused this stuck app in App Store.
Back to my solution to fix the issue, I removed the app DropCopy. Whala! The badge gone right away. Then I went to Purchased area, I can download it from there again.