Fix -Wunused-parameter in GraphicsObjectManager

[Capostrophic]

Oops, missed this when my nitpick in #35 was addressed.

/home/capostrophic/openscenegraph/include/osg/GLObjects: In member function «virtual void osg::GraphicsObjectManager::reportStats(unsigned int, osg::Stats&) const»:
/home/capostrophic/openscenegraph/include/osg/GLObjects:71:43: предупреждение: неиспользуемый параметр «frameNumber» [-Wunused-parameter]
   71 |         virtual void reportStats(unsigned frameNumber, Stats& stats) const {}
      |                                  ~~~~~~~~~^~~~~~~~~~~
/home/capostrophic/openscenegraph/include/osg/GLObjects:71:63: предупреждение: неиспользуемый параметр «stats» [-Wunused-parameter]
   71 |         virtual void reportStats(unsigned frameNumber, Stats& stats) const {}

[Capostrophic]

Ok, I'm merging this without a second approval because it's extra tough to get one in this repo and I really doubt the change is objectionable.

[AnyOldName3]

Capo, you are the second approval if you're merging it. We are not the same person.

[Capostrophic]

Second implicit or explicit approval with submitting the PR being a single implicit approval, second approval from someone who isn't the submitter. Semantics. Who cares.

[AnyOldName3]

Oh, I thought the submitter was the Gentoo guy.