[recipes] common: fixes blackout (higher order slice is an iterable itself so...

[recipes] common: fixes blackout (higher order slice is an iterable itself so we can not make this optional)

keras.py

@@ -192,7 +192,6 @@ def Blackout(ref, slic, name=None):
     shape = ref.shape[1:]
     dtype = ref.dtype
     mask = np.ones(shape, dtype=dtype)
-    slic = slic if isinstance(slic, Iterable) else (slic,)
     for _slic in slic:
         mask[_slic] = 0
     return tf.keras.layers.Lambda((lambda x: x * mask), name=name)