REFAC: remove the OTB_OPENCV_3 cmake variable

Modules/ThirdParty/OpenCV/otb-module-init.cmake

@@ -26,13 +26,6 @@ if("${OpenCV_VERSION}" VERSION_LESS "2.4.0")
     "it may not be fully compatible with OTB")
 endif()
 
-# OTB_OPENCV_3 is true for OpenCV 3 and 4
-if(OpenCV_VERSION_MAJOR GREATER_EQUAL 3)
-set(OTB_OPENCV_3 1)
-else()
-set(OTB_OPENCV_3 0)
-endif()
-
 if(OpenCV_VERSION_MAJOR EQUAL 4)
 set(OTB_OPENCV_4 1)
 else()

Modules/ThirdParty/OpenCV/src/otb_opencv_api.h.in

@@ -20,7 +20,6 @@
 #ifndef otb_opencv_api_h
 #define otb_opencv_api_h
 
-#cmakedefine OTB_OPENCV_3
 #cmakedefine OTB_OPENCV_4
 
 #endif