Remove double TaxableMixin inheritage

Sale line inherits already of TaxableMixin in sale module.

issue11092
review372951002

sale.py

@@ -4,7 +4,6 @@
 from decimal import Decimal
 
 from trytond.i18n import gettext
-from trytond.modules.account.tax import TaxableMixin
 from trytond.pool import Pool, PoolMeta
 
 from .exceptions import BadRequest
@@ -171,18 +170,9 @@ class SaleShipmentCost(metaclass=PoolMeta):
             self.carrier = carrier.id if carrier else None
 
 
-class Line(TaxableMixin, metaclass=PoolMeta):
+class Line(metaclass=PoolMeta):
     __name__ = 'sale.line'
 
-    @property
-    def taxable_lines(self):
-        return [(
-                getattr(self, 'taxes', None) or [],
-                getattr(self, 'unit_price', None) or Decimal(0),
-                getattr(self, 'quantity', None) or 0,
-                None,
-                )]
-
     @property
     def vsf_tax_amount(self):
         return sum(