drop rss-feed from frontpage

The RSS-feed generated for the frontpage contains all pages as well as news, which isn't what people expect from RSS feeds.

Additionally, if we produce an RSS-feed for the top-level, we produce the following warning using W3C's Feed Validator:

Implausible date: Mon, 01 Jan 0001 00:00:00 +0000

This is produced for https://www.mesa3d.org/website/, which isn't a news-post, so it doesn't really have the concept of a publication date.

So, let's just drop the RSS feed for the home-page. People can find the link to the RSS feed from the news-page instead.