[Accuracy diff No.79] Fix accuracy diff for paddle.combinations API

[ooooo-create]

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PR Category

Execute Infrastructure

PR Types

Improvements

Description

日志显示反向梯度为 None，没有梯度回传 删除部分特判 paddle.empty(shape=[0, r], dtype=x.dtype) 代码，实际上去掉代码的运行结果还是正确的（torch 代码上也没有特判https://github.com/pytorch/pytorch/blob/d632cf2cc9aac8ab0e03d1537982265e42be95e5/aten/src/ATen/native/Itertools.cpp#L60-L73

• PadddleAPITest 测试通过

TODO

• [ ] GPU 环境下单测失败，怀疑是 masked_select_grad 的 0 size 支持问题，问题反馈到 https://github.com/PaddlePaddle/Paddle/pull/73180 等修复之后试试看能不能解决