Remove the CrowdAuthentication extension.
Remove the Auth_remoteuser extension.
Remove the LdapAuthentication extension.
Remove the NewUserMessage extension.
Remove the NssMySQLAuth extension.
Remove the ArticleFeedback extension.
Remove the GlobalAuth extension.
Remove the TwitterLogin extension.
Remove the OpenID and LinkOpenID extensions.
Remove the AuthorProtect extension.
Remove the ConfirmAccount extensions.
Remove the SemanticSignup extension.
Remove unused LibmemcachedSessionHandler.
Merge pull request #5540 from Wikia/release-254-helios-preparations-release-dec-3

Cleanups as part of the Helios project.