python: eliminate pylint warnings

Tested with:
- pylint 1.9.1

samples/python/tutorial_code/Histograms_Matching/histogram_equalization/EqualizeHist_Demo.py

@@ -18,7 +18,7 @@ src = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
 ## [Convert to grayscale]
 
 ## [Apply Histogram Equalization]
-dst = cv.equalizeHist(src);
+dst = cv.equalizeHist(src)
 ## [Apply Histogram Equalization]
 
 ## [Display results]

samples/python/tutorial_code/imgProc/Smoothing/smoothing.py

@@ -88,7 +88,7 @@ def main(argv):
 def display_caption(caption):
     global dst
     dst = np.zeros(src.shape, src.dtype)
-    rows, cols, ch = src.shape
+    rows, cols, _ch = src.shape
     cv.putText(dst, caption,
                 (int(cols / 4), int(rows / 2)),
                 cv.FONT_HERSHEY_COMPLEX, 1, (255, 255, 255))

samples/python/tutorial_code/imgProc/threshold/threshold.py

@@ -33,7 +33,7 @@ if src is None:
     print('Could not open or find the image: ', args.input)
     exit(0)
 # Convert the image to Gray
-src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY);
+src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
 ## [load]
 
 ## [window]

samples/python/tutorial_code/imgProc/threshold_inRange/threshold_inRange.py

@@ -94,7 +94,7 @@ while True:
         break
 
     frame_HSV = cv.cvtColor(frame, cv.COLOR_BGR2HSV)
-    frame_threshold = cv.inRange(frame_HSV, (low_H, low_S, low_V), (high_H, high_S, high_V));
+    frame_threshold = cv.inRange(frame_HSV, (low_H, low_S, low_V), (high_H, high_S, high_V))
     ## [while]
 
     ## [show]