Updated mediawiki/extensions
Project: mediawiki/extensions/Flow  afcbacb58f6ee70b8d3397b0d1dc1dc65cf693ec

Remove history engine stub

It's been there as an empty stub since the beginning of the frontend
rewrite.

Also fix adjacent doc issue.

Change-Id: I83db1623d994fc4b0843409584779992156f8399