fix gcc 5+ compilation -Werror=unused-variable

@jsola can you please compile on your laptop (clang) ?

src/yaml/processor_image_yaml.cpp

@@ -84,8 +84,8 @@ static ProcessorParamsBasePtr createProcessorParamsImage(const std::string & _fi
 }
 
 // Register in the SensorFactory
-const bool registered_prc_image_feature_par = ProcessorParamsFactory::get().registerCreator("IMAGE FEATURE", createProcessorParamsImage);
-const bool registered_prc_image_landmark_par = ProcessorParamsFactory::get().registerCreator("IMAGE LANDMARK", createProcessorParamsImage);
+const bool WOLF_UNUSED registered_prc_image_feature_par = ProcessorParamsFactory::get().registerCreator("IMAGE FEATURE", createProcessorParamsImage);
+const bool WOLF_UNUSED registered_prc_image_landmark_par = ProcessorParamsFactory::get().registerCreator("IMAGE LANDMARK", createProcessorParamsImage);
 
 
 }