Remove all using directives for STL namespace and members

Made all STL usages explicit to be able automatically find all usages of
particular class or function.

samples/cpp/tutorial_code/features2D/SURF_FlannMatcher.cpp

@@ -11,6 +11,7 @@
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/nonfree/features2d.hpp"
 
+using namespace std;
 using namespace cv;
 
 void readme();