Enable linear roots in UpdateAllMirrorsWorker

In this commit we're removing the ff
`linear_mirrors_worker_roots` and enabling the
linear version of `UpdateAllMirrorsWorker`.

Changelog: changed
EE: true

config/feature_flags/development/linear_mirrors_worker_roots.yml

----
-name: linear_mirrors_worker_roots
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/76735
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/348415
-milestone: '14.7'
-type: development
-group: group::authentication and authorization
-default_enabled: false

ee/app/workers/update_all_mirrors_worker.rb

@@ -144,16 +144,11 @@ class UpdateAllMirrorsWorker # rubocop:disable Scalability/IdempotentWorker
 
   # rubocop: disable CodeReuse/ActiveRecord
   def root_namespaces_sql
-    namespace = Namespace.where('id = projects.namespace_id')
-
-    if Feature.enabled?(:linear_mirrors_worker_roots, default_enabled: :yaml)
-      namespace.roots.as_ids
-    else
-      Gitlab::ObjectHierarchy
-        .new(namespace)
-        .roots
-        .select(:id)
-    end.to_sql
+    Namespace
+      .where('id = projects.namespace_id')
+      .roots
+      .as_ids
+      .to_sql
   end
   # rubocop: enable CodeReuse/ActiveRecord
 end

ee/spec/workers/update_all_mirrors_worker_spec.rb

@@ -187,40 +187,28 @@ RSpec.describe UpdateAllMirrorsWorker do
       let(:unlicensed_projects) { [unlicensed_project1, unlicensed_project2, unlicensed_project3, unlicensed_project4] }
 
       context 'when using SQL to filter projects' do
-        shared_examples 'examples checking namespace plans' do
-          before do
-            allow(subject).to receive(:check_mirror_plans_in_query?).and_return(true)
-          end
-
-          context 'when capacity is in excess' do
-            it 'schedules all available mirrors' do
-              schedule_mirrors!(capacity: 4)
-
-              expect_import_scheduled(licensed_project1, licensed_project2, public_project)
-              expect_import_not_scheduled(*unlicensed_projects)
-            end
-          end
+        before do
+          allow(subject).to receive(:check_mirror_plans_in_query?).and_return(true)
+        end
 
-          context 'when capacity is exactly sufficient' do
-            it 'does not include unlicensed non-public projects in batches' do
-              # We expect that all three eligible projects will be
-              # included in the first batch because the query will only
-              # return eligible projects.
-              expect(subject).to receive(:pull_mirrors_batch).with(hash_including(batch_size: 6)).and_call_original.once
+        context 'when capacity is in excess' do
+          it 'schedules all available mirrors' do
+            schedule_mirrors!(capacity: 4)
 
-              schedule_mirrors!(capacity: 3)
-            end
+            expect_import_scheduled(licensed_project1, licensed_project2, public_project)
+            expect_import_not_scheduled(*unlicensed_projects)
           end
         end
 
-        it_behaves_like 'examples checking namespace plans'
+        context 'when capacity is exactly sufficient' do
+          it 'does not include unlicensed non-public projects in batches' do
+            # We expect that all three eligible projects will be
+            # included in the first batch because the query will only
+            # return eligible projects.
+            expect(subject).to receive(:pull_mirrors_batch).with(hash_including(batch_size: 6)).and_call_original.once
 
-        context 'when feature flag ' do
-          before do
-            stub_feature_flags(linear_mirrors_worker_roots: false)
+            schedule_mirrors!(capacity: 3)
           end
-
-          it_behaves_like 'examples checking namespace plans'
         end
       end