Callback delegate, invoked when a file descriptor should be removed from the set of file descriptors being monitored for events.


- fd (Int32)
- The file descriptor to stop monitoring.
- user_data (IntPtr)
- User data pointer specified in SetPollfdNotifiers(MonoUsbSessionHandle, PollfdAddedDelegate, PollfdRemovedDelegate, IntPtr) call.

After returning from this callback, do not use that file descriptor again.