Cleanup api_caching_releases feature flag

This commit cleans up the api_caching_releases feature
flag.

changelogs/unreleased/cleanup-api_caching_releases-feature-flag.yml

+---
+title: Improve the performance of Release LIST v4 API endpoint by short-interval caching
+merge_request: 61223
+author:
+type: performance

config/feature_flags/development/api_caching_releases.yml

----
-name: api_caching_releases
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60194
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/329861
-milestone: '13.12'
-type: development
-group: group::release
-default_enabled: false

lib/api/releases.rb

@@ -33,21 +33,17 @@ module API
       get ':id/releases' do
         releases = ::ReleasesFinder.new(user_project, current_user, declared_params.slice(:order_by, :sort)).execute
 
-        if Feature.enabled?(:api_caching_releases, user_project, default_enabled: :yaml)
-          # We cache the serialized payload per user in order to avoid repeated renderings.
-          # Since the cached result could contain sensitive information,
-          # it will expire in a short interval.
-          present_cached paginate(releases),
-                         with: Entities::Release,
-                         # `current_user` could be absent if the releases are publicly accesible.
-                         # We should not use `cache_key` for the user because the version/updated_at
-                         # context is unnecessary here.
-                         cache_context: -> (_) { "user:{#{current_user&.id}}" },
-                         expires_in: 5.minutes,
-                         current_user: current_user
-        else
-          present paginate(releases), with: Entities::Release, current_user: current_user
-        end
+        # We cache the serialized payload per user in order to avoid repeated renderings.
+        # Since the cached result could contain sensitive information,
+        # it will expire in a short interval.
+        present_cached paginate(releases),
+                        with: Entities::Release,
+                        # `current_user` could be absent if the releases are publicly accesible.
+                        # We should not use `cache_key` for the user because the version/updated_at
+                        # context is unnecessary here.
+                        cache_context: -> (_) { "user:{#{current_user&.id}}" },
+                        expires_in: 5.minutes,
+                        current_user: current_user
       end
 
       desc 'Get a single project release' do

spec/requests/api/releases_spec.rb

@@ -185,22 +185,6 @@ RSpec.describe API::Releases do
       3.times { get api("/projects/#{project.id}/releases", maintainer) }
     end
 
-    context 'when api_caching_releases feature flag is disabled' do
-      before do
-        stub_feature_flags(api_caching_releases: false)
-      end
-
-      it 'serializes releases everytime' do
-        create_list(:release, 2, project: project)
-
-        expect(API::Entities::Release)
-          .to receive(:represent).with(kind_of(ActiveRecord::Relation), any_args)
-          .exactly(5).times
-
-        5.times { get api("/projects/#{project.id}/releases", maintainer) }
-      end
-    end
-
     context 'when tag does not exist in git repository' do
       let!(:release) { create(:release, project: project, tag: 'v1.1.5') }