Fix MSVC2013-compiler warnings with QT_NO_FILESYSTEMWATCHER

dialogs\qfilesystemmodel.cpp(203,1667,1680): C4189: 'd': local variable is initialized but not referenced
dialogs\qfilesystemmodel.cpp(1547,1720,1847): C4100: 'variable': unreferenced formal parameter

Change-Id: Ic3cef264dcd0b939748bec914eb9c29f86f6ed0e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>