Unscheduling vs Cancelling scheduled jobs

Problem

Unschedule action is very similar to the cancel button. We might be able to simplify. Let's discuss.

Sources

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21767#note_104143003:

I don't like making "Cacnel" button's behavior implicit. "Cancel" button has a clear intention that it cancels the job, this means delayed jobs should go to "Cacnel" state directly, instead of transiting to "Manual" state.

So I'd say "Unschedule" button is still necessary that it indicates a clear intention that it transits to "Manual" state.

https://gitlab.slack.com/archives/CC9JAV5G8/p1538390054000100