Remove `ci_pipeline_rewind_iid` feature flag

It is no longer
needed.

app/services/ci/create_pipeline_service.rb

@@ -82,8 +82,7 @@ module Ci
       schedule_head_pipeline_update if pipeline.persisted?
 
       # If pipeline is not persisted, try to recover IID
-      pipeline.reset_project_iid unless pipeline.persisted? ||
-          Feature.disabled?(:ci_pipeline_rewind_iid, project, default_enabled: true)
+      pipeline.reset_project_iid unless pipeline.persisted?
 
       pipeline
     end

config/feature_flags/development/ci_pipeline_rewind_iid.yml

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

spec/services/ci/create_pipeline_service_spec.rb

@@ -731,30 +731,11 @@ RSpec.describe Ci::CreatePipelineService do
             .and_call_original
         end
 
-        context 'when ci_pipeline_rewind_iid is enabled' do
-          before do
-            stub_feature_flags(ci_pipeline_rewind_iid: true)
-          end
-
-          it 'rewinds iid' do
-            result = execute_service
-
-            expect(result).not_to be_persisted
-            expect(internal_id.last_value).to eq(0)
-          end
-        end
-
-        context 'when ci_pipeline_rewind_iid is disabled' do
-          before do
-            stub_feature_flags(ci_pipeline_rewind_iid: false)
-          end
-
-          it 'does not rewind iid' do
-            result = execute_service
+        it 'rewinds iid' do
+          result = execute_service
 
-            expect(result).not_to be_persisted
-            expect(internal_id.last_value).to eq(1)
-          end
+          expect(result).not_to be_persisted
+          expect(internal_id.last_value).to eq(0)
         end
       end
     end