Removed CV_EXPORTS from all template classes (that I could find).

It doesn't make sense to export template classes, since there's no way
the user can learn that it can import them. In fact, it is somewhat
deleterious, because every module will export every instantiation
that it uses, but doesn't inline.

modules/features2d/include/opencv2/features2d.hpp

@@ -961,7 +961,7 @@ struct CV_EXPORTS Hamming
 
 typedef Hamming HammingLUT;
 
-template<int cellsize> struct CV_EXPORTS HammingMultilevel
+template<int cellsize> struct HammingMultilevel
 {
     enum { normType = NORM_HAMMING + (cellsize>1) };
     typedef unsigned char ValueType;