Remove deprecated MediaWiki::articleFromTitle() and WikiPage::createUpdates()

No uses found in core or Gerrit extensions.

* MediaWiki::articleFromTitle() (deprecated in 1.18)
* WikiPage::createUpdates() (deprecated in 1.18)

Change-Id: I689249b579ee89f883b97fdb4ac79fb3502c45dc
Merge "Remove deprecated MediaWiki::articleFromTitle() and WikiPage::createUpdates()"