Shift the second dimension of x right by one.

def shift_right_2d(x, pad_value=None):
  """Shift the second dimension of x right by one."""
  if pad_value is None:
    shifted_targets = tf.pad(x, [[0, 0], [1, 0]])[:, :-1]
  else:
    shifted_targets = tf.concat([pad_value, x], axis=1)[:, :-1]
  return shifted_targets