Don't know about if its good for the kidneys or not, but avoiding excessive salt is a good thing for all our body parts.
There are no zero salt foods, just foods with higher levels of natural salt and foods with a lot of added sodium (more highly processed foods). Stick to preparing your food at home with natural ingredients, avoid adding salt if possible (but not slavishly and use sea salt or natural salt when you do--our bodies need a certain amount, but usually there is enough or close to it in natural foods anyway), avoid fast food at all costs, read labels for sodium and other "salt" words and avoid those that list it early in the ingredient list. This is an easy one to accomplish with a little study and commitment. Sugar should be treated the same way and is much harder to control. Biggest "food" to avoid is soft drinks. Tons of added sodium and sugar and none of it good for you.