ENH: Use the vtkTestingObjectFactory.

This allows me to remove some boilerplate code, which still allowing
interactive use of the tests.

Charts/Testing/Cxx/TestGLSL.cxx

@@ -103,11 +103,7 @@ int TestGLSL( int argc, char * argv [] )
   view->GetRenderWindow()->SetMultiSamples(0);
 
   int retVal = vtkRegressionTestImage(view->GetRenderWindow());
-  if(retVal == vtkRegressionTester::DO_INTERACTOR)
-    {
-    view->GetInteractor()->Initialize();
-    view->GetInteractor()->Start();
-    }
+  view->GetInteractor()->Start();
 
   if (test->IsCompiled)
     {

Charts/Testing/Cxx/TestLinePlot.cxx

@@ -79,12 +79,6 @@ int TestLinePlot( int argc, char * argv [] )
   //Finally render the scene and compare the image to a reference image
   view->GetRenderWindow()->SetMultiSamples(0);
   int retVal = vtkRegressionTestImageThreshold(view->GetRenderWindow(), 25);
-  //int retVal = vtkRegressionTestImage(view->GetRenderWindow());
-  if(retVal == vtkRegressionTester::DO_INTERACTOR)
-    {
-    view->GetInteractor()->Initialize();
-    view->GetInteractor()->Start();
-    }
-
+  view->GetInteractor()->Start();
   return !retVal;
 }