Deprecated techdocs use cases and linting

These are actually not redundant because @lucas42 is using them in a product.  We should support them in techdocs, possibly via some kind of label or badge.  I've asked him to comment on what kind of UI features would be useful.  In the meantime we should at least define them as custom use cases in techdocs, so that Luke can change his dep from colours to techdocs and update the use case names.