Drop the engines RSS feed

The engines listing is a handful of curated pages, not a stream — no feed
needed. Removes the route, controller action, RssService#engines_feed and
the footer link. The WikiService#pages alias stays (blog/howtos feeds use
it).

apps/api/config/routes.rb

@@ -11,7 +11,6 @@ Rails.application.routes.draw do
     get "rss/blog",             to: "rss#blog"
     get "rss/releases",         to: "rss#releases"
     get "rss/howtos",           to: "rss#howtos"
-    get "rss/engines",          to: "rss#engines"
   end
 
   # Utolsó sor: a host route-jai nyernek, a katalógus-útvonalakat