index-extra.php still includes Magpie

[nacin]

The widgets use Simplepie, so we just need to remove the unnecessary include.

Remove inclusion of rss.php

Hmm, a Trac db locked error caused the attachment to be renamed on the second attempt, as if 12051.diff already existed.

(In [12869]) Don't load deprecated magpie for dashboard. Props nacin. fixes #12051