Remove _boundingBoxComputed from sceneutil's riggeometry.cpp

Recent versions of OpenSceneGraph have no _boundingBoxComputed, which is why building TES3MP with them causes an error. As expected, recent versions of OpenMW do not use _boundingBoxComputed either.

components/sceneutil/riggeometry.cpp

@@ -288,12 +288,8 @@ void RigGeometry::updateBounds(osg::NodeVisitor *nv)
     }
 
     _boundingBox = box;
-    _boundingBoxComputed = true;
-#if OSG_VERSION_GREATER_OR_EQUAL(3,3,3)
-    // in OSG 3.3.3 and up Drawable inherits from Node, so has a bounding sphere as well.
     _boundingSphere = osg::BoundingSphere(_boundingBox);
     _boundingSphereComputed = true;
-#endif
     for (unsigned int i=0; i<getNumParents(); ++i)
         getParent(i)->dirtyBound();
 }