You don't have to use iCloud on your computer, but if you log in you will get rid of the update flag, and then you can turn off all the iCloud stuff you don't want to use.
It's a bit backwards, but it'll work.
I use iCloud on all my iOS devices, but not really on the desktops. Only since I've been working from home have I found it useful to have my reminders & messages coming up on the desktop instead of the iphone/ipad.