For some reason, IOHIDDeviceRegisterRemovalCallback() no longer works on
10.15+, so an app will crash once trying to poll a device that doesn't
exist anymore. Thankfully, there is the alternative solution of using
IOHIDManagerRegisterDeviceRemovalCallback(). This just required a little
rearranging of the callback code, as well as keeping track of the
connection between IOHIDDeviceRefs and IOKitInputDevices so we actually
know which device to remove.
Closes#847
Donny Lawrence
rdb