Rita, I recall reading that, at one time, it was believed that water was detrimental for marathoners. Whiskey was served instead. Those had to be some interesting marathons. I'm not sure water or any other drink was ever banned, just not used because the benefit wasn't understood.
As for de-fizzed Coke, as recently as the 80s it was pretty widely used. I remember Coach Conway telling me that he picked up the idea from someone (I can't recall who right now) and used it in all of his marathons. Honestly, if you look at the ingredients, it's not all that different from some sports drinks. Lots of water and a source of sugar.