remove unused config

config/danbooru_default_config.rb

@@ -432,10 +432,6 @@ module Danbooru
     end
 
     # listbooru options - see https://github.com/r888888888/listbooru
-    def listbooru_enabled?
-      false
-    end
-
     def listbooru_server
     end
 

test/unit/moderator/tag_batch_change_test.rb

@@ -8,7 +8,6 @@ module Moderator
     def setup
       super
       mock_saved_search_service!
-      Danbooru.config.stubs(:listbooru_enabled?).returns(true)
       Danbooru.config.stubs(:listbooru_auth_key).returns("blahblahblah")
       Danbooru.config.stubs(:listbooru_server).returns("http://localhost:3001")
     end

test/unit/saved_search_test.rb

@@ -8,7 +8,6 @@ class SavedSearchTest < ActiveSupport::TestCase
   def setup
     super
     mock_saved_search_service!
-    Danbooru.config.stubs(:listbooru_enabled?).returns(true)
     Danbooru.config.stubs(:listbooru_auth_key).returns("blahblahblah")
     Danbooru.config.stubs(:listbooru_server).returns("http://localhost:3001")
   end