Remove unused functions

renderLine16_Blend(), renderLine16_Decal(), renderLine32_Blend(), renderLine32_Decal()
clipLine()
frand()
drawRectangle() and drawLine()

remove unused private fields

source/Irrlicht/COpenGLDriver.h

@@ -522,8 +522,6 @@ namespace video
 		#endif
 
 		IContextManager* ContextManager;
-
-		E_DEVICE_TYPE DeviceType;
 	};
 
 } // end namespace video