Updated mediawiki/extensions
Project: mediawiki/extensions/CentralNotice  6dd53be10551ed23fbd86908d550d3adf9667a1f

remove outdated README

Nothing in here was true any more.  We could use a new README, and
it should link to the full documentation on mediawiki.org.

Change-Id: Ieaadb53d1034481f03997f3dde39b715eaedfabc