Quantize models have unused ValueInfos

[justinchuby]

Some quantized models have value infos that are not defined in the graph. For example, MNIST-12-int8 has {'Pooling66_Output_0', 'ReLU114_Output_0', 'Parameter193_reshape1', 'Plus30_Output_0', 'Convolution28', 'Convolution28_Output_0', 'Plus214_Output_0_MatMul', 'ReLU32_Output_0', 'Plus112_Output_0', 'Times212_Output_0', 'Convolution110_Output_0'} but they don't exist in the model.