Duplicate flash info messages on some user settings pages.

[MemoryLeakDeath]

Some user preferences pages show a duplicate flash message at the top of the screen due to there being a copy of the flash alert div on both the app.html.eex page and the user-sidebar.html.eex page. Only the user settings pages that use a Controller.live_render() call in UserSettingsController.ex exhibit this issue. You can reproduce it easily by going to the "Notifications" settings page then changing from dark to light mode or vice versa.