FEATURE: Remove support for legacy navigation menu (#23752)

Why this change?

Back in May 17 2023 along with the release of Discourse 3.1, we announced
on meta that the legacy hamburger dropdown navigation menu is
deprecated and will be dropped in Discourse 3.2. This is the link to the announcement
on meta: https://meta.discourse.org/t/removing-the-legacy-hamburger-navigation-menu-option/265274

## What does this change do?

This change removes the `legacy` option from the `navigation_menu` site
setting and migrates existing sites on the `legacy` option to the
`header dropdown` option.

All references to the `legacy` option in code and tests have been
removed as well.

app/models/admin_dashboard_data.rb

@@ -207,8 +207,7 @@ class AdminDashboardData
                       :unreachable_themes,
                       :watched_words_check,
                       :google_analytics_version_check,
-                      :translation_overrides_check,
-                      :legacy_navigation_menu_check
+                      :translation_overrides_check
 
     register_default_scheduled_problem_checks
 
@@ -368,12 +367,6 @@ class AdminDashboardData
     end
   end
 
-  def legacy_navigation_menu_check
-    if SiteSetting.navigation_menu == "legacy"
-      I18n.t("dashboard.legacy_navigation_menu_deprecated", base_path: Discourse.base_path)
-    end
-  end
-
   def image_magick_check
     if SiteSetting.create_thumbnails && !system("command -v convert >/dev/null;")
       I18n.t("dashboard.image_magick_warning")

app/models/navigation_menu_site_setting.rb

@@ -3,7 +3,6 @@
 class NavigationMenuSiteSetting < EnumSiteSetting
   SIDEBAR = "sidebar"
   HEADER_DROPDOWN = "header dropdown"
-  LEGACY = "legacy"
 
   def self.valid_value?(val)
     values.any? { |v| v[:value] == val }
@@ -13,7 +12,6 @@ class NavigationMenuSiteSetting < EnumSiteSetting
     @values ||= [
       { name: "admin.navigation_menu.sidebar", value: SIDEBAR },
       { name: "admin.navigation_menu.header_dropdown", value: HEADER_DROPDOWN },
-      { name: "admin.navigation_menu.legacy", value: LEGACY },
     ]
   end
 

app/models/site_setting.rb

@@ -257,10 +257,6 @@ class SiteSetting < ActiveRecord::Base
     c.present? && c.to_i != SiteSetting.uncategorized_category_id.to_i
   end
 
-  def self.legacy_navigation_menu?
-    SiteSetting.navigation_menu == "legacy"
-  end
-
   protected
 
   def self.clear_cache!

app/models/topic_tracking_state.rb

@@ -43,7 +43,7 @@ class TopicTrackingState
     return unless topic.regular?
 
     tag_ids, tags = nil
-    tag_ids, tags = topic.tags.pluck(:id, :name).transpose if SiteSetting.tagging_enabled
+    tag_ids, tags = topic.tags.pluck(:id, :name).transpose if include_tags_in_report?
 
     payload = {
       last_read_post_number: nil,
@@ -71,7 +71,7 @@ class TopicTrackingState
     return unless topic.regular?
 
     tag_ids, tags = nil
-    tag_ids, tags = topic.tags.pluck(:id, :name).transpose if SiteSetting.tagging_enabled
+    tag_ids, tags = topic.tags.pluck(:id, :name).transpose if include_tags_in_report?
 
     message = {
       topic_id: topic.id,
@@ -276,11 +276,7 @@ class TopicTrackingState
   end
 
   def self.include_tags_in_report?
-    SiteSetting.tagging_enabled && (@include_tags_in_report || !SiteSetting.legacy_navigation_menu?)
-  end
-
-  def self.include_tags_in_report=(v)
-    @include_tags_in_report = v
+    SiteSetting.tagging_enabled
   end
 
   # Sam: this is a hairy report, in particular I need custom joins and fancy conditions
@@ -340,7 +336,7 @@ class TopicTrackingState
   end
 
   def self.tags_included_wrapped_sql(sql)
-    return <<~SQL if SiteSetting.tagging_enabled && TopicTrackingState.include_tags_in_report?
+    return <<~SQL if include_tags_in_report?
         WITH tags_included_cte AS (
           #{sql}
         )

app/models/user.rb

@@ -2048,7 +2048,6 @@ class User < ActiveRecord::Base
   private
 
   def set_default_sidebar_section_links(update: false)
-    return if SiteSetting.legacy_navigation_menu?
     return if staged? || bot?
 
     if SiteSetting.default_navigation_menu_categories.present?