Remove async_update_pages_config feature flag

Removing this flag means that all updates to Pages configuration will
happen in Sidekiq, none in Puma.

app/models/pages_domain.rb

@@ -249,11 +249,7 @@ class PagesDomain < ApplicationRecord
     return if usage_serverless?
     return unless pages_deployed?
 
-    if Feature.enabled?(:async_update_pages_config, project)
-      run_after_commit { PagesUpdateConfigurationWorker.perform_async(project_id) }
-    else
-      Projects::UpdatePagesConfigurationService.new(project).execute
-    end
+    run_after_commit { PagesUpdateConfigurationWorker.perform_async(project_id) }
   end
   # rubocop: enable CodeReuse/ServiceClass
 

app/services/projects/update_service.rb

@@ -144,11 +144,7 @@ module Projects
     def update_pages_config
       return unless project.pages_deployed?
 
-      if Feature.enabled?(:async_update_pages_config, project)
-        PagesUpdateConfigurationWorker.perform_async(project.id)
-      else
-        Projects::UpdatePagesConfigurationService.new(project).execute
-      end
+      PagesUpdateConfigurationWorker.perform_async(project.id)
     end
 
     def changing_pages_https_only?

config/feature_flags/development/async_update_pages_config.yml

----
-name: async_update_pages_config
-introduced_by_url:
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/230695
-group: 'team::Scalability'
-type: development
-default_enabled: false

spec/models/pages_domain_spec.rb

@@ -354,16 +354,6 @@ RSpec.describe PagesDomain do
       domain.destroy!
     end
 
-    it 'delegates to Projects::UpdatePagesConfigurationService when not running async' do
-      stub_feature_flags(async_update_pages_config: false)
-
-      service = instance_double('Projects::UpdatePagesConfigurationService')
-      expect(Projects::UpdatePagesConfigurationService).to receive(:new) { service }
-      expect(service).to receive(:execute)
-
-      create(:pages_domain, project: project)
-    end
-
     it "schedules a PagesUpdateConfigurationWorker" do
       expect(PagesUpdateConfigurationWorker).to receive(:perform_async).with(project.id)
 

spec/services/projects/update_service_spec.rb

@@ -412,32 +412,6 @@ RSpec.describe Projects::UpdateService do
 
         subject
       end
-
-      context 'when `async_update_pages_config` is disabled' do
-        before do
-          stub_feature_flags(async_update_pages_config: false)
-        end
-
-        it 'calls Projects::UpdatePagesConfigurationService when pages are deployed' do
-          project.mark_pages_as_deployed
-
-          expect(Projects::UpdatePagesConfigurationService)
-            .to receive(:new)
-                  .with(project)
-                  .and_call_original
-
-          subject
-        end
-
-        it "does not update pages config when pages aren't deployed" do
-          project.mark_pages_as_not_deployed
-
-          expect(Projects::UpdatePagesConfigurationService)
-            .not_to receive(:new)
-
-          subject
-        end
-      end
     end
 
     context 'when updating #pages_https_only', :https_pages_enabled do