Tweak QObject::deleteLater() documentation a bit

The Qt 4.8 reference is not relevant. And mentioning that calling the
function more than once is safe, or why that is, is strange, as users
should still treat the object as something that will go away soon.

Pick-to: 6.7
Change-Id: Icf24aa8ffe079e35351006dd77063df48a596fab
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qobject.cpp

@@ -2428,10 +2428,6 @@ void QObject::removeEventFilter(QObject *obj)
     );
     \endcode
 
-    \note It is safe to call this function more than once; when the
-    first deferred deletion event is delivered, any pending events for the
-    object are removed from the event queue.
-
     \sa destroyed(), QPointer
 */
 void QObject::deleteLater()