Fix UAS unit test

Destroyed signal must have been working incorrectly in the past.

src/qgcunittest/UASUnitTest.cc

@@ -301,7 +301,6 @@ void UASUnitTest::signalWayPoint_test()
 
 void UASUnitTest::signalUASLink_test()
 {
-
     QSignalSpy spy(uas, SIGNAL(modeChanged(int,QString,QString)));
     uas->setMode(2, 0);
     QCOMPARE(spy.count(), 0);// not solve for UAS not receiving message from UAS
@@ -347,7 +346,7 @@ void UASUnitTest::signalUASLink_test()
     delete link2;
 
     QCOMPARE(LinkManager::instance()->getLinks().count(), 1);
-    QCOMPARE(uas->getLinks()->count(), 2);
+    QCOMPARE(uas->getLinks()->count(), 1);
 
     QCOMPARE(static_cast<LinkInterface*>(LinkManager::instance()->getLinks().at(0))->getId(),
              static_cast<LinkInterface*>(uas->getLinks()->at(0))->getId());

src/uas/UAS.cc

@@ -3375,8 +3375,13 @@ void UAS::addLink(LinkInterface* link)
 void UAS::removeLink(QObject* object)
 {
     // Be careful of the fact that by the time this signal makes it through the queue
-    // the link object has already been destructed.
-    links->removeAt(links->indexOf((LinkInterface*)object));
+    // the link object has already been destructed. So no dynamic_cast for example.
+    
+    LinkInterface* link = (LinkInterface*)object;
+    
+    int index = links->indexOf(link);
+    Q_ASSERT(index != -1);
+    links->removeAt(index);
 }
 
 /**