Remove some unused variables in render_gl.cpp. https://tracker.physiomeproject.org/show_bug.cgi?id=3726
Remove some unused variables in render_gl.cpp. https://tracker.physiomeproject.org/show_bug.cgi?id=3726

OpenCMISS/zinc,hsorby/zinc,OpenCMISS/zinc,OpenCMISS/zinc,OpenCMISS/zinc,hsorby/zinc,hsorby/zinc,hsorby/zinc