♻️(backend) deprecate has_consent_to_terms for Order model

From now on, the terms and conditions (CGV in French) must be
specific to each organization. We can no longer use a global
version for the entire platform. These terms will be included
directly in the contract's context, so the Order model no longer
needs to track user acceptance, as this will happen during contract
signing.

Fix #816

src/backend/joanie/tests/core/test_models_order.py

@@ -1120,18 +1120,6 @@ def test_models_order_has_unsigned_contract_signature(self):
         )
         self.assertFalse(order.has_unsigned_contract)
 
-    def test_models_order_has_unsigned_contract_product_contract_definition(self):
-        """
-        Check that the `has_unsigned_contract` property returns True
-        if the order's contract is not signed by student.
-        """
-        order = factories.OrderFactory(
-            product__contract_definition=factories.ContractDefinitionFactory()
-        )
-        self.assertTrue(order.has_unsigned_contract)
-        with self.assertRaises(Contract.DoesNotExist):
-            order.contract  # pylint: disable=pointless-statement
-
     def test_models_order_has_consent_to_terms_should_raise_deprecation_warning(self):
         """
         Due to the refactoring of `has_consent_to_terms` attribute, it is now a deprecated field.

src/backend/joanie/tests/swagger/admin-swagger.json

@@ -7760,4 +7760,4 @@
             }
         }
     }
-}
+}

src/backend/joanie/tests/swagger/swagger.json

@@ -7213,4 +7213,4 @@
             }
         }
     }
-}
+}