Move wgWarnNotRecentlyUpdatedPages configuration block to agora

Summary:
Hierarchy is setting / wiki / value, wiki has been omitted.

This is a follow-up for 0d52ff032892.

Ref T1893

Test Plan: $wgWarnNotRecentlyUpdatedPages on mw shell agora

Reviewers: dereckson

Maniphest Tasks: T1893

Differential Revision: https://devcentral.nasqueron.org/D3166