Drop Python2 support.

samples/python/contours.py

@@ -9,26 +9,18 @@ Usage:
 A trackbar is put up which controls the contour level from -3 to 3
 '''
 
-# Python 2/3 compatibility
-from __future__ import print_function
-import sys
-PY3 = sys.version_info[0] == 3
-
-if PY3:
-    xrange = range
-
 import numpy as np
 import cv2 as cv
 
 def make_image():
     img = np.zeros((500, 500), np.uint8)
     black, white = 0, 255
-    for i in xrange(6):
+    for i in range(6):
         dx = int((i%2)*250 - 30)
         dy = int((i/2.)*150)
 
         if i == 0:
-            for j in xrange(11):
+            for j in range(11):
                 angle = (j+5)*np.pi/21
                 c, s = np.cos(angle), np.sin(angle)
                 x1, y1 = np.int32([dx+100+j*10-80*c, dy+100-90*s])