Remove unnecessary import of Warning.

doc/examples/plot_line_hough_transform.py

@@ -1,4 +1,4 @@
-"""
+r"""
 =============================
 Straight line Hough transform
 =============================

skimage/__init__.py

@@ -88,9 +88,7 @@ test_verbose = _functools.partial(test, verbose=True)
 test_verbose.__doc__ = test.__doc__
 
 
-from exceptions import Warning as _Warning
-
-class _Log(_Warning):
+class _Log(Warning):
     pass
 
 class _FakeLog(object):

skimage/_shared/utils.py

@@ -1,7 +1,6 @@
 import warnings
 import functools
 import sys
-from exceptions import Warning
 
 from . import six