[Feature flag] Remove `group_vulnerabilities_optimized_query` FF

A modified query was created for the group-level vulnerability report
export to resolve [time-out issues][0] for large exports

The new query resolves the timeout issues. However, for our larger
customers the export will still fail for other reasons related to a
large group

Further work will need to be done to completely unblock large
vulnerability report exports

resolves: https://gitlab.com/gitlab-org/gitlab/-/issues/426394

[0]:https://gitlab.com/gitlab-org/gitlab/-/issues/392885
[1]:https://gitlab.com/gitlab-org/gitlab/-/issues/432548

EE: true
Changelog: changed

ee/app/services/vulnerability_exports/export_service.rb

@@ -56,7 +56,7 @@ def exporter
     end
 
     def vulnerabilities
-      if exportable.is_a?(Group) && ::Feature.enabled?(:group_vulnerabilities_optimized_query, exportable)
+      if exportable.is_a?(Group)
         scope = ::Vulnerability.unscoped # rubocop:disable CodeReuse/ActiveRecord
 
         opts = {

ee/config/feature_flags/development/group_vulnerabilities_optimized_query.yml

----
-name: group_vulnerabilities_optimized_query
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/127180
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/426394
-milestone: '16.5'
-type: development
-group: group::threat insights
-default_enabled: false

ee/spec/services/vulnerability_exports/export_service_spec.rb

@@ -137,17 +137,6 @@
 
             expect(rows.count).to eq(group.vulnerabilities.without_archived_projects.count)
           end
-
-          context 'when group_vulnerabilities_optimized_query is disabled' do
-            before do
-              stub_feature_flags(group_vulnerabilities_optimized_query: false)
-            end
-
-            it 'delegates vulnerability lookup to the finder' do
-              export
-              expect(mock_vulnerability_finder_service_object).to have_received(:execute)
-            end
-          end
         end
       end
     end