Remove Solr2Rss Special Page from Answers Wikis

I think this extension is a good candidate for removal for the following reasons:

* Not highly used
* Only included in answers wikis
* Hasn't worked for over two months, and neither product nor community has said anything. The only reason we know it's broken is because fatal errors show up in the logs once in a great while when it's being accessed.

I think that we can safely drop support for this extension.

I'm especially interested in the opinions of @owend and @federico-lox on this one.