you ignore it. the same way you ignore the print button you can't use because you don't have an AirPrint compat printer.
Screen space is limited on a phone. Sure you can ignore it, but it's using up valuable screen space. In a few years we'll have to scroll through 4-5 pages of "share" options, 80% of which we don't use?
Come on. This is the sort of thinking that makes systems gradually turn to suck.