Remove the unreachable epic search result partial

What does this MR do and why?

app/views/search/_results_list.html.haml has rendered the epics scope through search/results/work_item since 23ccbd31be26, and nothing else renders search/results/epic. This MR deletes the unreachable EE partial ee/app/views/search/results/_epic.html.haml and the translation string that only it used (%{group_name}&%{epic_iid} · created %{epic_created} by %{author}) from locale/gitlab.pot. The spec the issue mentions no longer exists on master.

References

• Resolves #628829

Differences

Before: Dead partial and an orphaned .pot entry.

After: Both removed; search results render identically.

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