Remove all of GitLab CI for GitLab 9.0

The remaining references are:

Left in upgrades so you can walk through upgrading from old to new The gitlab_ci config object still exists for the 4 keys that are used in gitlab.yml

Closes: #792 (closed)

Testing (including running CI jobs using a CI secret):

• Fresh install
• Upgrade from 8.16 to this branch
• Upgrade from 8.10 to this branch (the secrets were still namespaced as CI, this might break things?)
• Upgrade from 8.0 to this branch (GitLab CI merged into GitLab)
• Upgrade from 7.14 (GitLab CI bundled but separate)