[t2t] Remove the workaround for "ValueError: prediction values with "inputs: DatasetToSingleElement:0" must be from the default graph.".
[t2t] Remove the workaround for "ValueError: prediction values with "inputs: DatasetToSingleElement:0" must be from the default graph.".

If not run on TPU this workaround is unnecessary but sometimes breaks running code with an error: "Cannot use 'while/Pad' as input to 'Identity' because 'while/Pad' is in a while loop." (encountered while running e.g. universal_transformer).

PiperOrigin-RevId: 267424524

tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor