Remove dev app from lib-user

[mcbouslog]

Remove dev app (https://github.com/zooniverse/front-end-monorepo/tree/master/packages/lib-user/dev) from lib-user. The dev app was very helpful with initial lib-user development, but I think it would be preferable to rely on storybook and app-root in dev mode for subsequent work on lib-user to minimize maintenance and potential development issues.