Remove `Repository#version` method and tests

What does this MR do?

Removes Repository#version method and tests

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

no

Why was this MR needed?

Feature was removed after redesign ~ 1 year ago by https://gitlab.com/gitlab-org/gitlab-ce/commit/d192f921c17561c82943bc803875ba6bf11fd8ce. This is dead code.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• 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?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/24251