Update __init__.py

A little optimization: Now, don't need to import "sys" and will also work if Skimage imported from a byte-compilled Python distribution.

skimage/io/__init__.py

@@ -10,7 +10,6 @@ from .collection import *
 
 from ._io import *
 from ._image_stack import *
-import sys
 
 
 reset_plugins()
@@ -59,5 +58,5 @@ def _update_doc(doc):
 
     return doc
 
-if sys.flags.optimize < 2:
+if __doc__ is not None:
     __doc__ = _update_doc(__doc__)