fix(assets import): Ensure old datasource ids are not referenced in imported charts (#25086)

(cherry picked from commit b240b795b5)

tests/integration_tests/commands_test.py

@@ -141,6 +141,9 @@ class TestImportAssetsCommand(SupersetTestCase):
         dataset = chart.table
         assert str(dataset.uuid) == dataset_config["uuid"]
 
+        assert chart.query_context is None
+        assert json.loads(chart.params)["datasource"] == dataset.uid
+
         database = dataset.database
         assert str(database.uuid) == database_config["uuid"]