explore/posts/intro: remove page.

This was an alternate frontpage that contained a list of previews of the
most popular tags. This page was never linked from anywhere and it was
unknown by most users.

config/routes.rb

@@ -49,7 +49,6 @@ Rails.application.routes.draw do
         get :viewed
         get :searches
         get :missed_searches
-        get :intro
       end
     end
   end
@@ -400,8 +399,6 @@ Rails.application.routes.draw do
   get "/static/contact" => "static#contact", :as => "contact"
   get "/static/dtext_help" => "static#dtext_help", :as => "dtext_help"
 
-  get "/intro" => redirect("/explore/posts/intro")
-
   root :to => "posts#index"
 
   get "*other", :to => "static#not_found"