Enable linear ParticipantsService ancestors queries

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

Changelog: added

app/services/projects/participants_service.rb

@@ -36,17 +36,9 @@ module Projects
     private
 
     def project_members_through_invited_groups
-      groups_with_ancestors = if ::Feature.enabled?(:linear_participants_service_ancestor_scopes, current_user, default_enabled: :yaml)
-                                visible_groups.self_and_ancestors
-                              else
-                                Gitlab::ObjectHierarchy
-                                  .new(visible_groups)
-                                  .base_and_ancestors
-                              end
-
       GroupMember
         .active_without_invites_and_requests
-        .with_source_id(groups_with_ancestors.pluck_primary_key)
+        .with_source_id(visible_groups.self_and_ancestors.pluck_primary_key)
     end
 
     def visible_groups

config/feature_flags/development/linear_participants_service_ancestor_scopes.yml

----
-name: linear_participants_service_ancestor_scopes
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/70684
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/341348
-milestone: '14.4'
-type: development
-group: group::access
-default_enabled: false

spec/services/projects/participants_service_spec.rb

@@ -207,13 +207,5 @@ RSpec.describe Projects::ParticipantsService do
     end
 
     it_behaves_like 'return project members'
-
-    context 'when feature flag :linear_participants_service_ancestor_scopes is disabled' do
-      before do
-        stub_feature_flags(linear_participants_service_ancestor_scopes: false)
-      end
-
-      it_behaves_like 'return project members'
-    end
   end
 end