Crash on process exit when the evdevtouch plugin is loaded and has active devices

During normal process exit, QTouchDevicePrivate already cleans up all registered touch devices via a qAddPostRoutine. This happens before the plugins get cleaned up, so by the time the destructor for the plugin's QEvdevTouchScreenHandler gets called the device is already deleted, and calling unregisterTouchDevice() in the destructor again results in a double delete and crash.

Unregistering the device in the destructor isn't needed anyway for any use case. The touch device will already be properly unregistered and deleted
if the device gets removed, as the fd will report the read error
in readData() and unregisterTouchDevice() will get called there. That's the only case where devices can be removed dynamically during regular execution, for all other cases the cleanup will happen during the QApplication shutdown.

Note that there's already a long-standing change request for this bug: https://codereview.qt-project.org/#/c/142561/

but it's been stalled and I haven't been able to get a decision. This needs to be adressed one way or another asap.