Remove ci_pipeline_ensure_iid_on_skip feature flag

MR: gitlab.com/gitlab-org/gitlab/-/merge_requests/61231
Issue: gitlab.com/gitlab-org/gitlab/-/issues/327661

Changelog: performance

changelogs/unreleased/remove_flag_ci_pipeline_ensure_iid_on_skip.yml

+---
+title: Ensure iid is set before skipping ci pipeline
+merge_request: 61231
+author:
+type: performance

config/feature_flags/development/ci_pipeline_ensure_iid_on_skip.yml

----
-name: ci_pipeline_ensure_iid_on_skip
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/59342
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/327661
-milestone: '13.12'
-type: development
-group: group::code review
-default_enabled: false

lib/gitlab/ci/pipeline/chain/skip.rb

@@ -12,12 +12,10 @@ module Gitlab
           def perform!
             if skipped?
               if @command.save_incompleted
-                if Feature.enabled?(:ci_pipeline_ensure_iid_on_skip, @pipeline.project, default_enabled: :yaml)
-                  # Project iid must be called outside a transaction, so we ensure it is set here
-                  # otherwise it may be set within the state transition transaction of the skip call
-                  # which it will lock the InternalId row for the whole transaction
-                  @pipeline.ensure_project_iid!
-                end
+                # Project iid must be called outside a transaction, so we ensure it is set here
+                # otherwise it may be set within the state transition transaction of the skip call
+                # which it will lock the InternalId row for the whole transaction
+                @pipeline.ensure_project_iid!
 
                 @pipeline.skip
               end

spec/lib/gitlab/ci/pipeline/chain/skip_spec.rb

@@ -40,18 +40,6 @@ RSpec.describe Gitlab::Ci::Pipeline::Chain::Skip do
 
       step.perform!
     end
-
-    context 'when the ci_pipeline_ensure_iid_on_save feature flag is off' do
-      before do
-        stub_feature_flags(ci_pipeline_ensure_iid_on_skip: false)
-      end
-
-      it 'does not call ensure_project_iid explicitly' do
-        expect(pipeline).not_to receive(:ensure_project_iid!)
-
-        step.perform!
-      end
-    end
   end
 
   context 'when pipeline has not been skipped' do