In my opinion that belt isn't rubbing on anything. It still has the printing on it, you can clearly see it's a Dayco belt and the blue print on this area looks as new. Seems to me like it's not running quite square because the water pump plate has pushed the tensioner away so has a small strip which isn't making contact with the tensioner, that's all. The discolouration you think is from rubbing looks like the standard texture the belts have before they smooth off from following over the tensioner etc.