Remove unused arbitrary_sql_order_clause.

Unused since f87c71c.

app/logical/post_sets/base.rb

@@ -39,19 +39,5 @@ module PostSets
     def presenter
       raise NotImplementedError
     end
-
-    def arbitrary_sql_order_clause(ids, table_name)
-      if ids.empty?
-        return "#{table_name}.id desc"
-      end
-
-      conditions = []
-
-      ids.each_with_index do |x, n|
-        conditions << "when #{x} then #{n}"
-      end
-
-      "case #{table_name}.id " + conditions.join(" ") + " end"
-    end
   end
 end

config/initializers/active_record_extensions.rb

@@ -33,22 +33,6 @@ module Danbooru
           connection.__send__(method_name, sanitize_sql_array([sql, *params]))
         end
       end
-
-      def arbitrary_sql_order_clause(ids, table_name = nil)
-        table_name = self.class.table_name if table_name.nil?
-
-        if ids.empty?
-          return "#{table_name}.id desc"
-        end
-
-        conditions = []
-
-        ids.each_with_index do |x, n|
-          conditions << "when #{x} then #{n}"
-        end
-
-        "case #{table_name}.id " + conditions.join(" ") + " end"
-      end
     end
   end
 end