remove unused variable

Change-Id: Ic6455f080fae211d7919d9f6ea35cdbda3ca3757

chart2/source/view/inc/GL3DRenderer.hxx

@@ -253,8 +253,6 @@ private:
 
     glm::mat4 m_3DView;
 
-    glm::mat4 m_3DViewBack;
-
     glm::mat4 m_3DMVP;
 
     glm::mat4 m_TranslationMatrix;

chart2/source/view/main/GL3DRenderer.cxx

@@ -1418,7 +1418,6 @@ void OpenGL3DRenderer::CreateSceneBoxView()
                m_CameraInfo.cameraOrg, // and looks at the origin
                m_CameraInfo.cameraUp  // Head is up (set to 0,-1,0 to look upside-down)
                );
-    m_3DViewBack = m_3DView;
 }
 
 void OpenGL3DRenderer::ProcessUnrenderedShape()