The news of “The Late Show’s” cancellation by CBS doesn’t just end a franchise that had, to this point, lasted more than 30 years. It looks like the beginning of the end of an entire category of television. With one network now opting out of late-night talk entirely, how long will it be before the genre just goes away? CBS announced the cancellation nearly a full year before it is to take effect, making current host Stephen Colbert a lame duck of sorts; he will continue hosting the show through May 2026, at which point it will simply disappear. Observers...