undecorated_table_name was moved and refactored

guides/source/active_support_core_extensions.md

@@ -1431,11 +1431,10 @@ As the previous example shows, Active Support knows some irregular plurals and u
 Active Record uses this method to compute the default table name that corresponds to a model:
 
 ```ruby
-# active_record/base.rb
+# active_record/model_schema.rb
 def undecorated_table_name(class_name = base_class.name)
   table_name = class_name.to_s.demodulize.underscore
-  table_name = table_name.pluralize if pluralize_table_names
-  table_name
+  pluralize_table_names ? table_name.pluralize : table_name
 end
 ```