I'm not sure I follow what you want to do or why?

First thing is you cannot remove a thread.  Only an admin can do that.  You can delete your replies but if you start a thread only an admin can remove it.

Are you talking about the "Your Active Threads" button results?  It takes care of itself. Don't worry about it.  Check it every day or two because at times it gets interesting. Someone will find an old discussion and jump in not realizing it was 11 years old (Yes, I've had it happen).  It pops up on the active thread list and you're asking yourself "When did we talk about that?" only to realize the date.