Unwanted creation of extra memory for `data_consistency` in gpuNUFFT

[chaithyagr]

https://github.com/mind-inria/mri-nufft/blob/ddd342aef78861e2a9324573b33eca434a4ac16b/src/mrinufft/operators/interfaces/gpunufft.py#L694

This memory isnt really needed as we already have obs_data saved... This can help make it more memory efficient