Do not reference to the QAbstractNativeEventFilter documentation

1) It is not strictly necessary since the method argument type is already
designed for clickable here. Thereby, it is just a duplication.

2) It is not done inside the removeNativeEventFilter, so it is not consistent
now.

3) Similarly, the following documentation in 4.8 did not have another explicit
reference to the documentation of the EventFilter typedef:
EventFilter QCoreApplication::setEventFilter ( EventFilter filter )

Change-Id: I45fd42a03b16fd173fca9d734a7771e804d577d8
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: David Faure <faure@kde.org>

src/corelib/kernel/qcoreapplication.cpp

@@ -2188,7 +2188,7 @@ void QCoreApplication::installNativeEventFilter(QAbstractNativeEventFilter *filt
     It is always safe to remove an event filter, even during event
     filter activation (i.e. from the nativeEventFilter() function).
 
-    \sa installNativeEventFilter(), QAbstractNativeEventFilter
+    \sa installNativeEventFilter()
     \since 5.0
 */
 void QCoreApplication::removeNativeEventFilter(QAbstractNativeEventFilter *filterObj)