🔥 refactor(custom_lists.py): remove unused vectorstores_type_to_cls_dict variable

🔨 refactor(vector_store/base.py): refactor VectorstoreCreator to use import_class from langflow.interface.importing.utils
The `vectorstores_type_to_cls_dict` variable was not being used, so it was removed. The `VectorstoreCreator` class was refactored to use the `import_class` function from `langflow.interface.importing.utils` instead of importing it directly. This improves the code's readability and maintainability.