Fix to exit of adopted thread watcher in Windows

Fix to exit of adopted thread watcher in Windows

Don't register the thread handle and QThread object pointer to watch list
for adopted thread watcher thread in Windows. Otherwise the watcher thread
will never exit and can't clean up its own QThreadData and QAdoptedThread
object.

Task-number: QTBUG-23961

Change-Id: Ia84326cf3cfd978d2b003ccc1bb6861db950e899
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>