Superfluous: it’s there for Android, but I believe that sans-serif will normally resolve to that anyway.
(I’m not certain about that, and can’t confirm it as I don’t have ready access to Chrome on Android but I got the impression some years ago that Chrome on Android uses the system font, which is Roboto. But even apart from that, the general idea is “stop specifying specific fonts and let the browser do its thing and the user get their chosen fonts, unless what the browser does by default is too bad, like Courier New for monospace”.)