Security: How to log out remotely from Backup and synchronization?

You can only achieve this by Changing your password.

A little more detail:

In addition to the browser, you can enable verification in two steps, enable two-step verification pause the synchronization in all Chrome browsers where you have logged in and it will disconnect you from all web sessions, but it will not disconnect you from Backup and sync.

Second, you can not remove computers in security settings, just mobile devices.

If you go to Gmail, click on "Details" in the lower right corner (under "Last account activity"), then click on "Sign out of all other Gmail web sessions", only the session will be closed Google websites in browsers that have not signed in to Chrome. Therefore, if you signed in to Chrome on another computer and do so, Chrome will re-login to Google websites.