[REM] delivery: remove unused field/method

- The volume field of stock.picking extended in delivery was unused,
-> remove it.
- The commit 2ff3749064, add
the 'check_packages_are_identical', which is never used.
- Remove useless variable 'res' of print_return_label in stock_picking

task-2201168

closes odoo/odoo#46516

Related: odoo/upgrade#866
Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/delivery/models/stock_picking.py

@@ -78,7 +78,6 @@ class StockPicking(models.Model):
     carrier_price = fields.Float(string="Shipping Cost")
     delivery_type = fields.Selection(related='carrier_id.delivery_type', readonly=True)
     carrier_id = fields.Many2one("delivery.carrier", string="Carrier", check_company=True)
-    volume = fields.Float(copy=False, digits='Volume')
     weight = fields.Float(compute='_cal_weight', digits='Stock Weight', store=True, help="Total weight of the products in the picking.", compute_sudo=True)
     carrier_tracking_ref = fields.Char(string='Tracking Reference', copy=False)
     carrier_tracking_url = fields.Char(string='Tracking URL', compute='_compute_carrier_tracking_url')
@@ -172,7 +171,7 @@ class StockPicking(models.Model):
 
     def print_return_label(self):
         self.ensure_one()
-        res = self.carrier_id.get_return_label(self)
+        self.carrier_id.get_return_label(self)
 
     def _add_delivery_cost_to_so(self):
         self.ensure_one()
@@ -222,16 +221,6 @@ class StockPicking(models.Model):
             picking.message_post(body=msg)
             picking.carrier_tracking_ref = False
 
-    def check_packages_are_identical(self):
-        '''Some shippers require identical packages in the same shipment. This utility checks it.'''
-        self.ensure_one()
-        if self.package_ids:
-            packages = [p.packaging_id for p in self.package_ids]
-            if len(set(packages)) != 1:
-                package_names = ', '.join([str(p.name) for p in packages])
-                raise UserError(_('You are shipping different packaging types in the same shipment.\nPackaging Types: %s' % package_names))
-        return True
-
     def _get_estimated_weight(self):
         self.ensure_one()
         weight = 0.0