Don't track the sharable bit upon detach

"Unsharables", given they can't be shared, don't need to detach, so skip the
check altogether and don't try to propagate the flag. It shouldn't be.

Change-Id: Icc483401d5a57708b43d64bd3cebc66c6b934815
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qarraydata.h

@@ -101,10 +101,6 @@ struct Q_CORE_EXPORT QArrayData
     AllocationOptions detachFlags() const
     {
         AllocationOptions result;
-#if QT_SUPPORTS(UNSHARABLE_CONTAINERS)
-        if (!ref.isSharable())
-            result |= Unsharable;
-#endif
         if (capacityReserved)
             result |= CapacityReserved;
         return result;