Enable linear ApplicationSettings ancestors queries

In this commit, we're removing the feature flag
`linear_application_setting_ancestor_scopes` to allow
ApplicationSettings using linear queries.

Changelog: added
EE: true

config/feature_flags/development/linear_application_setting_ancestor_scopes.yml

----
-name: linear_application_setting_ancestor_scopes
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/70579
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/341346
-milestone: '14.4'
-type: development
-group: group::access
-default_enabled: false

ee/app/models/ee/application_setting.rb

@@ -385,14 +385,9 @@ module EE
 
     def elasticsearch_limited_project_exists?(project)
       project_namespaces = ::Namespace.where(id: project.namespace_id)
-      indexed_namespaces = if ::Feature.enabled?(:linear_application_setting_ancestor_scopes, default_enabled: :yaml)
-                             project_namespaces.self_and_ancestors
-                           else
-                             ::Gitlab::ObjectHierarchy.new(project_namespaces).base_and_ancestors
-                           end
-
-      indexed_namespaces = indexed_namespaces.joins(:elasticsearch_indexed_namespace)
-      indexed_namespaces = ::Project.where('EXISTS (?)', indexed_namespaces)
+      self_and_ancestors_namespaces = project_namespaces.self_and_ancestors.joins(:elasticsearch_indexed_namespace)
+
+      indexed_namespaces = ::Project.where('EXISTS (?)', self_and_ancestors_namespaces)
       indexed_projects = ::Project.where('EXISTS (?)', ElasticsearchIndexedProject.where(project_id: project.id))
 
       ::Project

ee/spec/models/application_setting_spec.rb

@@ -457,14 +457,6 @@ RSpec.describe ApplicationSetting do
           end
 
           it_behaves_like 'whether the project is indexed'
-
-          context 'when feature flag :linear_application_setting_ancestor_scopes is disabled' do
-            before do
-              stub_feature_flags(linear_application_setting_ancestor_scopes: false)
-            end
-
-            it_behaves_like 'whether the project is indexed'
-          end
         end
       end