[Backport 3.0] Remove not functioning SitemapFeedBasedOnHstSitemap and SiteMapBasedOnHstSiteMapResource

A client has troubles with the SitemapFeedBasedOnHstSitemap compnent, probably because of the spawning of threads (4 by default) within a single HST request.

See also wko from HIPPLUG-710:

This doesn't look right. An HstComponent should run in its own thread only. If you need a backend work like this with multiple threads, then you'd better create a dedicated service under the hood and let the component simply read the (cached) result generated by the dedicated service. That's how it should work.