First off, there is no such thing as "devolution" (except a certain '80s pop band). Evolution simply means "change." The opposite of change is "stasis."
Secondly, neither chimps nor humans make vitamin C for the very simple reason that we both get plenty of it through natural sources. When the mutation turning off our vitamin C maker appeared, it had absolutely no effect on the survival of the original owner, so saying it made the critter less adapted to its environment is clearly mistaken.
Playing with the meaning of words when shown that your example was wrong. Evolution is the addition of traits enabling a creature or a species to grow more complex. This is clearly necessary for evolutionary theory to be true since the only way the higher species could have evolved from single celled bacteria and lower species as Darwin and evolutionists say, is by adding new characteristics and more complexity.
Now taking away information, taking away capabilities, taking away complexity as in the example with vitamin c clearly could not be the path taken for more complex species. Therefore it is de-volution. And while it may not have been necessary all the time, it certainly would have made man and ape more fit for many environments in which vitamin c was not readily available. So here what we have is not only an example of de-volution but also an example of survival of the less fit.