Use linear version ApplicationSettings#elasticsearch_limited_namespaces

config/feature_flags/development/linear_application_settings_elasticsearch_limited_namespaces.yml

----
-name: linear_application_settings_elasticsearch_limited_namespaces
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/68931
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/339438
-milestone: '14.3'
-type: development
-group: group::access
-default_enabled: false

ee/app/models/ee/application_setting.rb

@@ -235,11 +235,7 @@ module EE
 
       return namespaces if ignore_descendants
 
-      if ::Feature.enabled?(:linear_application_settings_elasticsearch_limited_namespaces, default_enabled: :yaml)
       namespaces.self_and_descendants
-      else
-        ::Gitlab::ObjectHierarchy.new(namespaces).base_and_descendants
-      end
     end
 
     def pseudonymizer_available?

ee/spec/models/application_setting_spec.rb

@@ -440,7 +440,6 @@ RSpec.describe ApplicationSetting do
           let!(:child_group) { create(:group, parent: groups.first) }
           let!(:child_group_indexed_through_parent) { create(:group, parent: groups.last) }
 
-          shared_examples 'returns groups that are allowed to be indexed' do
           specify do
             create(:elasticsearch_indexed_namespace, namespace: child_group)
 
@@ -451,17 +450,6 @@ RSpec.describe ApplicationSetting do
           end
         end
 
-          it_behaves_like 'returns groups that are allowed to be indexed'
-
-          context 'when feature flag :linear_application_settings_elasticsearch_limited_namespaces is disabled' do
-            before do
-              stub_feature_flags(linear_application_settings_elasticsearch_limited_namespaces: false)
-            end
-
-            it_behaves_like 'returns groups that are allowed to be indexed'
-          end
-        end
-
         describe '#elasticsearch_indexes_project?' do
           shared_examples 'whether the project is indexed' do
             context 'when project is in a subgroup' do