Drop OpenCV2 support

Data/Baseline/OTB-Applications/Files/clDT_ConfMatQB1cv2.dt

.../Baseline/OTB-Applications/Files/clDT_ModelQB1-opencv2.dt

Data/Input/Classification/clDT_ModelQB1-opencv2.dt

Data/Input/Classification/clDT_ModelQB1cv2.dt

...ations/AppClassification/include/otbTrainDecisionTree.hxx

Modules/Applications/AppClassification/test/CMakeLists.txt

...earning/Supervised/include/otbBoostMachineLearningModel.h

...rning/Supervised/include/otbBoostMachineLearningModel.hxx

Modules/Learning/Supervised/include/otbCvRTreesWrapper.h

.../Supervised/include/otbDecisionTreeMachineLearningModel.h

...upervised/include/otbDecisionTreeMachineLearningModel.hxx

...rvised/include/otbKNearestNeighborsMachineLearningModel.h

...ised/include/otbKNearestNeighborsMachineLearningModel.hxx

...Supervised/include/otbNeuralNetworkMachineLearningModel.h

...pervised/include/otbNeuralNetworkMachineLearningModel.hxx

...g/Supervised/include/otbNormalBayesMachineLearningModel.h

...Supervised/include/otbNormalBayesMachineLearningModel.hxx

Modules/Learning/Supervised/include/otbOpenCVUtils.h

...Supervised/include/otbRandomForestsMachineLearningModel.h

...pervised/include/otbRandomForestsMachineLearningModel.hxx