Remove legacy artifact related code

What does this MR do?

Previously, we've dropped the usage of legacy artifact related in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24294 in order for ensuring it doesn't impact existing functionalities.

As we've confirmed that the change is not harmful at all, it's time to cleanup the old code.

• CE: Here
• EE: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/13128

What are the relevant issue numbers?

close https://gitlab.com/gitlab-org/gitlab-ce/issues/58595

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• [-] Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• [-] Security reports checked/validated by reviewer