Remove AA_DontUsePopupWindows

Back when 953f70179969b0beb797607c5454e36349319929 was first introduced,
we thought it would be a good idea to make popups in qtdeclarative use
popup windows by default, and then let users revert back to the old
behavior via setting an application attribute.

We eventually decided to go in a different direction, causing
AA_DontUsePopupWindows to no longer be needed.

More information can be found in here
823026646c62c7e3b42be1549fcb61debb468e60 in qtdeclarative.

Reverts 953f70179969b0beb797607c5454e36349319929

Pick-to: 6.8
Change-Id: I3c5054d92c4d8c38193e7e0c193f425b7414f6dd
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/corelib/global/qnamespace.h

@@ -462,7 +462,7 @@ namespace Qt {
         AA_DisableShaderDiskCache = 27,
         AA_DontShowShortcutsInContextMenus = 28,
         AA_CompressTabletEvents = 29,
-        AA_DontUsePopupWindows = 30,
+        // AA_DisableWindowContextHelpButton = 30, (in Qt 5)
         AA_DisableSessionManager = 31,
 
         // Add new attributes before this line

src/corelib/global/qnamespace.qdoc

@@ -279,11 +279,6 @@
            level windows, unless required by the implementation.
            This value was added in Qt 6.8.
 
-    \value AA_DontUsePopupWindows When this attribute is set, popups will always appear
-           as items in the scene, rather than having their own dedicated windows.
-           Setting this attribute will only affect Qt Quick applications.
-           This value was added in Qt 6.8.
-
     \omitvalue AA_AttributeCount
     \omitvalue AA_EnableHighDpiScaling
     \omitvalue AA_UseHighDpiPixmaps