I want to remove the automatic ratings from my songs:
However, they don't disappear after right-click->Rating->None
That is because the songs inherit an "estimate rating" from the album rating. If you want to remove these stars, you need to remove the album rating.
Click on the left of the stars from the album the song belongs:
they are now gone:
Apparently, this is the only way to change the album rating (the right-click menu doesn't show any options to change the rating).