What is the difference between the terms "obsolete" and "redundant"?
"Redundant" means someone or something else is already doing the work; "obsolete" means the job no longer needs to be done.
A redundant function can best be illustrated by a convenience store with five people on a shift; only one or two are actually needed to make the store perform profitably. Anybody else is redundant and should probably be fired.
An obsolete function is one that is simply no longer needed in any context, like a blacksmith or someone who delivers huge blocks of ice. We shifted away from a horse-and-icebox-based economy about a century ago and are not going back. It isn't so much a matter of having too many blacksmith shops in town, it's more a matter of not needing any of them.