[REM] mrp: remove _decrease_reserved_quanity

As `_do_unreserve` was rewrited, the `_decrease_reserved_quanity` method
isn't useful since its purpose was to avoid to unlink all stock moves
and it is what `_do_unreserve` cares about.

See 2e41338f42e2ef9f2ac2b3e73b274c4af242b28a

closes odoo/odoo#42582

Related: odoo/enterprise#7488
Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/mrp/models/mrp_production.py

@@ -677,9 +677,7 @@ class MrpProduction(models.Model):
             old_qty = move[0].product_uom_qty
             remaining_qty = move[0].raw_material_production_id.product_qty - move[0].raw_material_production_id.qty_produced
             if quantity > 0:
-                move[0]._decrease_reserved_quanity(quantity)
-                move[0].with_context(do_not_unreserve=True).write({'product_uom_qty': quantity})
-                move[0]._recompute_state()
+                move[0].write({'product_uom_qty': quantity})
                 move[0]._action_assign()
                 return move[0], old_qty, quantity
             else:

addons/mrp/models/stock_move.py

@@ -220,24 +220,6 @@ class StockMove(models.Model):
             production._action_cancel()
         return res
 
-    def _decrease_reserved_quanity(self, quantity):
-        """ Decrease the reservation on move lines but keeps the
-        all other data.
-        """
-        move_line_to_unlink = self.env['stock.move.line']
-        for move in self:
-            reserved_quantity = quantity
-            for move_line in self.move_line_ids:
-                if move_line.product_uom_qty > reserved_quantity:
-                    move_line.product_uom_qty = reserved_quantity
-                else:
-                    move_line.product_uom_qty = 0
-                    reserved_quantity -= move_line.product_uom_qty
-                if not move_line.product_uom_qty and not move_line.qty_done:
-                    move_line_to_unlink |= move_line
-        move_line_to_unlink.unlink()
-        return True
-
     def _prepare_phantom_move_values(self, bom_line, product_qty, quantity_done):
         return {
             'picking_id': self.picking_id.id if self.picking_id else False,