BUG #13821. Fixed vtkRenderingFreeTypeObjectFactory leaks.

In certain cases, vtkRenderingFreeTypeObjectFactory leaked when application
would quit (only in release builds with gcc).The problem was that while
vtkRenderingFreeType_AutoInit_Construct() would get called almost 11/12 times,
vtkRenderingFreeType_AutoInit_Destruct() was only getting called once. Which
resulted in vtkRenderingFreeTypeObjectFactory not being unregistered and hence
leaked.

Now the extra reference maintained to vtkRenderingFreeTypeObjectFactory instance
itself is unnecessary, since vtkObjectFactory::RegisterFactor() maintains a
reference and cleans the reference up when exiting. Cleaning this extra
reference overcomes the issue altogether.

Change-Id: I878a1c364ac3f1fd729ff06aa9eb3f4191e8660b
Merge topic '13821_fix_leaks_on_exit' into master

15549949 BUG #13821. Fixed vtkRenderingFreeTypeObjectFactory leaks.