How to remove a texture paint material slot?

I accidentally added a second slot which i didnt want and it has caused problems. I have exactly the same issue as described at this link (

However, the suggested action doesn’t work. Unlinking the datablock in the left window, saving and reloading the file just isnt working. It’s always still there after. Why can’t there just be a “remove” button as if it was a texture slot!!!?