Remove obsolete OS
- Ubuntu 14.04 - Removed in 11.11 - omnibus-gitlab!3192 (merged)
- openSUSE 42.3 - Removed in 12.0 - omnibus-gitlab!3469 (merged)
- openSUSE 15.0 - Removed in 12.6 - omnibus-gitlab!3753 (merged)
All of these are now outside our support window, and we can remove them.