Remove Main.RssFeeds page

This page lists all the places in your wiki that provides a RSS feed, acting as some help page. This is good. However:

• it's not linked anywhere from the navigation so you have to go directly to this page to see it. Thus it's not fulfilling its role of a help page
• it's not extension-ready, meaning that if you install an extension that provides a RSS feed it won't get added automatically to this page. Similarly if you remove one extension (like the search for example), you'll get a broken link.

As a consequence I think it's better to remove this page instead of moving it to the xwiki-platform-help application since:

• I don't feel it has such a high value
• It would require implementing a complex extension point mechanism so that applications can contribute RSS help which doesn't bring enough added value to justify the cost of doing it.