The avast self-defence module (avastUI, Settings, Troubleshooting) is what is blocking its removal. But it will also be a file in use as that is where lots of information on updates, etc. is stored and can be a valuable debug tool. I don't know why yours is large, mine was created in February and is only 410KB.
That said, if you are worried about the 2.9MB of hard disk space taken then you really are in trouble.
So I don't know why you would want to mess with it ?
If deleted it will be recreated.