Move windowcontainer example to manual test

Change-Id: I68b866bcc2659b90aad2c10dc06240674bf4a826
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit cd7995de57321854b1da01e07ba49e82520abfe3)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/widgets/CMakeLists.txt

@@ -27,6 +27,3 @@ endif()
 if(QT_FEATURE_cursor)
     add_subdirectory(mainwindows)
 endif()
-if(QT_FEATURE_opengl AND TARGET Qt6::Gui)
-    qt_internal_add_example(windowcontainer)
-endif()

examples/widgets/widgets.pro

@@ -22,9 +22,6 @@ SUBDIRS       = \
                 tutorials \
                 widgets
 
-qtHaveModule(gui):qtConfig(opengl): \
-    SUBDIRS += windowcontainer
-
 contains(DEFINES, QT_NO_CURSOR): SUBDIRS -= mainwindows
 !qtConfig(draganddrop): SUBDIRS -= draganddrop
 !qtConfig(animation): SUBDIRS -= animation