Reduce confusion in upgrade.md
Reduce confusion introduced with "Upgrade Notice for EE omnibus packages" in https://gitlab.com/gitlab-org/omnibus-gitlab/commit/7102c4b1f073a72993bc5fae897a45765346ea1e.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Reduce confusion introduced with "Upgrade Notice for EE omnibus packages" in https://gitlab.com/gitlab-org/omnibus-gitlab/commit/7102c4b1f073a72993bc5fae897a45765346ea1e.