NopDropout elimination replaces mask usage by input

[Flamefire]

In https://github.com/onnx/onnx/blob/ea694bf5cbccf34e08f36a8d9365d9011b72aeb4/onnx/optimizer/passes/eliminate_nop_dropout.h#L31 all outputs of the Dropout layer are replaced with inputs. However the 2nd output of that layer is mask which shall contain the mask. In the NoOp case this is all 1s and NOT the input

From https://github.com/onnx/onnx/issues/1672

[daquexian]

Thanks for your issue! I think you are right. I'll fix it soon