saved searches: remove option to disable saved searches.

Remove `SavedSearch.enabled?` checks. There's no need to make saved
searches optional, since Redis is now required to run Danbooru.

app/controllers/saved_searches_controller.rb

@@ -1,5 +1,4 @@
 class SavedSearchesController < ApplicationController
-  before_action :check_availability
   respond_to :html, :xml, :json, :js
   
   def index
@@ -39,12 +38,6 @@ class SavedSearchesController < ApplicationController
     CurrentUser.user.saved_searches
   end
 
-  def check_availability
-    if !SavedSearch.enabled?
-      raise NotImplementedError.new("Saved searches are not available.")
-    end
-  end
-
   def saved_search_params
     params.fetch(:saved_search, {}).permit(%i[query label_string disable_labels])
   end