[QA] Remove the :core tag since we're not using it anymore (!21436) · Merge requests · GitLab.org / GitLab FOSS · GitLab

What does this MR do?

Removes the :core tag since we're not using it anymore.

What are the relevant issue numbers?

Cleanup after https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20931.

Does this MR meet the acceptance criteria?

[-] Changelog entry added, if necessary
[-] Documentation created/updated
[-] Tests added for this feature/bug
Conforms to the code review guidelines
Conforms to the merge request performance guidelines
Conforms to the style guides
Conforms to the database guides