Remove bin/ci/upgrade.rb

What does this MR do?

While bin/ci/upgrade.rb was introduced from gitlab-org/gitlab-ci in !1204 (merged), it has never worked and so can now be removed to keep the bin directory clean.

Are there points in the code the reviewer needs to double check?

While I checked if this is not used in omnibus-gitlab, could you check any other place(s) to use this script if you know? (Even if used somewhere, it does not work at all 😭 )

Why was this MR needed?

As lib/upgrader.rb in gitlab-org/gitlab-ci has not been migrated to gitlab-ce, bin/ci/upgrade.rb can be removed.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [n/a] Documentation created/updated
• [n/a] API support added
• Tests
  • [n/a] Added for this feature/bug
  • All builds are passing
• [n/a] Conform by the merge request performance guides
• [n/a] Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #34207 (closed)