[qt6] Remove QtQuick.Window import

`QtQuick.Window` does not exist anymore with Qt6. QQuickWindow is now
directly part of the QtQuick module.

Author: cbentejac

meshroom/ui/qml/main.qml

@@ -4,7 +4,6 @@ import QtQuick
 import QtQuick.Controls
 import QtQuick.Dialogs
 import QtQuick.Layouts
-import QtQuick.Window
 import QtQml.Models
 
 import GraphEditor 1.0