Eliminate the need of ::testsing::ValuesIn() for CV_ENUM

Also cv::, cv::gpu:: and cv::ocl:: namespace prefixes can be safely omitted
inside CV_ENUM and CV_FLAGS

modules/gpu/test/test_optflow.cpp

@@ -333,7 +333,7 @@ namespace
 {
     IMPLEMENT_PARAM_CLASS(PyrScale, double)
     IMPLEMENT_PARAM_CLASS(PolyN, int)
-    CV_FLAGS(FarnebackOptFlowFlags, 0, cv::OPTFLOW_FARNEBACK_GAUSSIAN)
+    CV_FLAGS(FarnebackOptFlowFlags, 0, OPTFLOW_FARNEBACK_GAUSSIAN)
     IMPLEMENT_PARAM_CLASS(UseInitFlow, bool)
 }