This feature seems to be broken, I have enabled it and previous welcome messages stay up.
I actually did this originally, but then was confused a week later when I noticed they were supposed to be deleting, so I checked it and for some reason it was disabled when I know for a fact I enabled it. Anyways, I just enabled it again last night, and the previous welcome messages still stay up. The config shows the feature is still enabled.
This feature seems to be broken, I have enabled it and previous welcome messages stay up. I actually did this originally, but then was confused a week later when I noticed they were supposed to be deleting, so I checked it and for some reason it was disabled when I know for a fact I enabled it. Anyways, I just enabled it again last night, and the previous welcome messages still stay up. The config shows the feature is still enabled.