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.