Remove feature flag `status_page_attachments`

This feature flag has been enabled by defaults since 13.1
and no issues have been found so it's safe to assume it's not broken.

ee/app/services/status_page/publish_details_service.rb

@@ -40,8 +40,6 @@ module StatusPage
     end
 
     def publish_attachments(issue, user_notes)
-      return success unless attachements_enabled?
-
       StatusPage::PublishAttachmentsService.new(
         project: @project,
         issue: issue,
@@ -49,9 +47,5 @@ module StatusPage
         storage_client: storage_client
       ).execute
     end
-
-    def attachements_enabled?
-      Feature.enabled?(:status_page_attachments, @project, default_enabled: true)
-    end
   end
 end

ee/config/feature_flags/development/status_page_attachments.yml

----
-name: status_page_attachments
-introduced_by_url: 
-rollout_issue_url: 
-group: 
-type: development
-default_enabled: true

ee/spec/services/status_page/publish_details_service_spec.rb

@@ -39,17 +39,6 @@ RSpec.describe StatusPage::PublishDetailsService do
         allow(storage_client).to receive(:list_object_keys).and_return([])
       end
 
-      context 'when feature flag disabled' do
-        before do
-          stub_feature_flags(status_page_attachments: false)
-        end
-
-        it 'does not publish attachments and returns success' do
-          expect(StatusPage::PublishAttachmentsService).not_to receive(:new)
-          expect(subject.success?).to be true
-        end
-      end
-
       context 'when successful' do
         let(:success_response) { double(error?: false, success?: true) }