Remove `Snippet#expires_at`
This was removed from the interface in https://github.com/gitlabhq/gitlabhq/pull/6027 but its implementation lingered around for two years.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
This was removed from the interface in https://github.com/gitlabhq/gitlabhq/pull/6027 but its implementation lingered around for two years.