remove __future__ import in docstring, test=document_fix (#46890)

Author: SigureMo

python/paddle/distributed/spawn.py

@@ -474,8 +474,6 @@ def spawn(func, args=(), nprocs=-1, join=True, daemon=False, **options):
     Examples:
         .. code-block:: python
 
-            from __future__ import print_function
-
             import paddle
             import paddle.nn as nn
             import paddle.optimizer as opt