tests: delete the dockwidgets when each test ends

Will save us from doing manual cleanup.

tests/tst_docks.cpp

@@ -397,13 +397,8 @@ void TestDocks::tst_restoreSimple()
     dock3->morphIntoFloatingWindow(); // as it would take 1 event loop. Do it now so we can compare already.
 
     QCOMPARE(dock3->window()->pos(), dock3FloatingPoint);
-
-    // Cleanup
-    dock3->deleteLater();
-    QVERIFY(Testing::waitForDeleted(dock3));
 }
 
-
 void TestDocks::tst_doesntHaveNativeTitleBar()
 {
     // Tests that a floating window doesn't have a native title bar

tests/utils.h

@@ -101,13 +101,16 @@ struct EnsureTopLevelsDeleted
 
     ~EnsureTopLevelsDeleted()
     {
-        auto dr = DockRegistry::self();
+        qDeleteAll(DockRegistry::self()->floatingWindows(/*includeBeingDeleted=*/ true));
+        qDeleteAll(DockRegistry::self()->dockwidgets());
 
-        if (!dr->isEmpty())
+        if (!DockRegistry::self()->isEmpty()) {
+            auto dr = DockRegistry::self();
             qWarning() << "There's still top-level widgets present!"
                        << "\nfloatings:" << dr->floatingWindows(/*includeBeingDeleted=*/ true)
                        << "\nmainwindows:" << dr->mainWindowsNames()
                        << "\ndocks:" << dr->dockWidgetNames();
+        }
 
         // Other cleanup, since we use this class everywhere
         Config::self().setDockWidgetFactoryFunc(nullptr);