Remove duplicate metrics for group "editor"

What does this MR do and why?

#391729 (closed)

Approval from other teams on removing this metric

#391729 (comment 1285350524)

As part of removing duplicate metrics we have two metrics that does the same thing.

• usage_activity_by_stage_monthly.create.action_monthly_active_users_wiki_repo
• redis_hll_counters.source_code.wiki_action_monthly

After confirming with the team, I am removing usage_activity_by_stage_monthly.create.action_monthly_active_users_wiki_repo

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.