!6822 Remove Primitive from functional.__all__.

Merge pull request !6822 from liuxiao93/fix-op-list

mindspore/ops/functional.py

@@ -186,3 +186,4 @@ tensor_operator_registry.register('shape', shape)
 tensor_operator_registry.register('cast', cast)
 
 __all__ = [name for name in dir() if name[0] != "_"]
+__all__.remove('Primitive')