Revert "Lock wikis for MediaWiki upgrade"

Summary:
This reverts commit 4cd2b560e75cd42a401ce2f290f70cd1e31fea11.

Ref T2174

Test Plan: Edit a wiki page

Reviewers: philectro

Reviewed By: philectro

Maniphest Tasks: T2174

Differential Revision: https://devcentral.nasqueron.org/D3850