remove left/right from category

category.py

@@ -39,16 +39,16 @@ class Category(tree(separator='/'), ModelSQL, ModelView):
     company = fields.Many2One(string='Company', model_name='company.company',
         required=True, ondelete="RESTRICT")
     parent = fields.Many2One(string="Parent",
-        model_name='cashbook.category', ondelete='RESTRICT',
-        left='left', right='right')
+        model_name='cashbook.category', ondelete='RESTRICT')
     childs = fields.One2Many(string='Children', field='parent',
         model_name='cashbook.category')
-    left = fields.Integer(string='Left', required=True, select=True)
-    right = fields.Integer(string='Right', required=True, select=True)
 
     @classmethod
     def __register__(cls, module_name):
         super(Category, cls).__register__(module_name)
+        table = cls.__table_handler__(module_name)
+        table.drop_column('left')
+        table.drop_column('right')
         cls.migrate_sequence(module_name)
 
     @classmethod
@@ -83,14 +83,6 @@ class Category(tree(separator='/'), ModelSQL, ModelView):
     def default_company():
         return Transaction().context.get('company') or None
 
-    @staticmethod
-    def default_left():
-        return 0
-
-    @staticmethod
-    def default_right():
-        return 0
-
     @staticmethod
     def order_rec_name(tables):
         """ order by pos