[FIX] sale_order_line_position: remove deprecated function

sale_order_line_position/models/sale_order_line.py

@@ -35,7 +35,7 @@ def _add_next_position_on_new_line(self, vals_list):
         ]
         if sale_ids:
             ids = tuple(set(sale_ids))
-            self.flush_model()
+            self.env.flush_all()
             query = """
             SELECT order_id, max(position) FROM sale_order_line
             WHERE order_id in %s GROUP BY order_id;