Remove Defun for Fwd/Bak that wraps the cell_fn/cell_grad. They're redundant given that the callers (ForwardLoopBody/BackwardLoopBody) are already Defuns.
Remove Defun for Fwd/Bak that wraps the cell_fn/cell_grad. They're redundant given that the callers (ForwardLoopBody/BackwardLoopBody) are already Defuns.

PiperOrigin-RevId: 314366755

tensorflow/lingvo,tensorflow/lingvo,tensorflow/lingvo,tensorflow/lingvo