XPLM_API int        XPLMUnregisterDrawCallback(
                         XPLMDrawCallback_f   inCallback,    
                         XPLMDrawingPhase     inPhase,    
                         int                  inWantsBefore,    
                         void *               inRefcon);    

This routine unregisters a draw callback. You must unregister a callback for each time you register a callback if you have registered it multiple times with different refcons. The routine returns 1 if it can find the callback to unregister, 0 otherwise.

Note that this function will likely be removed during the X-Plane 11 run as part of the transition to Vulkan/Metal/etc. See the XPLMInstance API for future-proof drawing of 3-D objects.