Disabling pipelines in project settings doesn't disable scheduled pipelines.

I've realized today, that when someone will disable pipelines in project settings, this doesn't schedule a cancellation of all scheduled pipelines. This may and with a situation when thousands of CI/CD jobs are queued in GitLab, but:

• jobs are wasting resources since they need to be handled, but no one cares about the result,
• there is no easy way to delete them - if pipelines are disabled nor UI nor API allow to cancel a job.

I'm not sure if we should consider this as a gitlab-ce2278648 or a need for gitlab-ce2975007, but we should definitely force pipelines dropping when the feature is disabled in project's setting.