Other than Old school - find the news file and delete it - Is there, Should there be a way to delete the Avast News from within the news reader thingie? Say both individual updates and/or Clear all?
If you’re connected, probably you will receive all them again in next update :
Better is keep them 
If you’re in a computer without avast, I think, maybe, you get only the last ones. I’m not sure as I installed avast a long time ago 8)