MainApplicationWindow.qml: remove unused import of QtQuick.Dialogs

The module is not used anywhere in the file and breaks the client
on Windows.

GitLab: #1905
Change-Id: I7e4f6e3516a3fd88c7e150b3eeb70cab823d388b

src/app/MainApplicationWindow.qml

@@ -29,7 +29,6 @@ import "mainview/components"
 import "wizardview"
 import "commoncomponents"
 import QWindowKit
-import QtQuick.Dialogs
 
 ApplicationWindow {
     id: appWindow