remove unused variable iio

Author: brokkoli71

pims/image_reader.py

@@ -13,7 +13,6 @@ def imread(*args, **kwargs):  # Strip metadata for consistency.
         return np.asarray(iio.imread(*args, **kwargs))
 except ImportError:
     from skimage.io import imread
-    iio = None
 
 class ImageReader(FramesSequence):
     """Reads a single image into a length-1 reader.