It looks like this extension is defined in /usr/share/mime/packages/freedesktop.org.xml, which dpkg -S says is part of the shared-mime-info package. It's still there in oneiric too [1].
[1] http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/oneiric/shared-mime-info/oneiric/view/head:/freedesktop.org.xml
It looks like this extension is defined in /usr/share/ mime/packages/ freedesktop. org.xml, which dpkg -S says is part of the shared-mime-info package. It's still there in oneiric too [1].
[1] http:// bazaar. launchpad. net/~ubuntu- branches/ ubuntu/ oneiric/ shared- mime-info/ oneiric/ view/head: /freedesktop. org.xml