Revert the AddNotifiedOfOwnActivityToUsers migration
Safely reverts the migration added in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8836, which has been reverted via https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9974
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Safely reverts the migration added in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8836, which has been reverted via https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9974