QtIFW

Fix crash at the very end of install if admin rights needed in Windows

Removed the destroy call to RemoteClientPrivate object as that has been
destroyed at that point already in packagemanagercore destructor

Task-number: QTIFW-943
Change-Id: Ibb7b4f00842d780b32055dbdc3673d031c52a89a
Reviewed-by: Iikka Eklund <iikka.eklund@qt.io>