I'm having a hard time removing the password prompt off of an external hard disk I setup on my macbook. (I know the password)

So I set it up years ago, and know I don't know how to turn it off. It's not a huge deal, because I still know the password. It's just that I've been thinking of giving it to someone else.

I tried to decrypt it from the right click menu, as it says it is encrypted in the get info menu, but everytime I do it tells me:

"The target Core Storage volume is not encrypted."

What should I do?