DEV: Remove legacy user menu (#21308)

config/locales/server.en.yml

@@ -2413,7 +2413,6 @@ en:
     navigation_menu: "Determine which navigation menu to use. Sidebar and header navigation are customizable by users. Legacy option is available for backward compatibility."
     default_sidebar_categories: "Selected categories will be displayed under Sidebar's Categories section by default."
     default_sidebar_tags: "Selected tags will be displayed under Sidebar's Tags section by default."
-    enable_new_notifications_menu: "Enables the new notifications menu. Disabling this setting is deprecated. The new notifications menu is always used for non-legacy 'navigation menu' choices. <a href='https://meta.discourse.org/t/260358'>Learn more</a>"
     enable_experimental_hashtag_autocomplete: "EXPERIMENTAL: Use the new #hashtag autocompletion system for categories and tags that renders the selected item differently and has improved search"
     experimental_new_new_view_groups: 'EXPERIMENTAL: Enable a new topics list that combines unread and new topics and make the "Everything" link in the sidebar link to it.'
     enable_custom_sidebar_sections: "EXPERIMENTAL: Enable custom sidebar sections"

config/site_settings.yml

@@ -2132,8 +2132,6 @@ navigation:
     choices:
       - "default"
       - "unread_new"
-  enable_new_notifications_menu:
-    default: true
 
 embedding:
   embed_by_username: