Remove FF ci_use_merge_request_ref

This commit removes the FF

app/services/merge_requests/base_service.rb

@@ -89,7 +89,6 @@ module MergeRequests
     end
 
     def can_use_merge_request_ref?(merge_request)
-      Feature.enabled?(:ci_use_merge_request_ref, project, default_enabled: true) &&
       !merge_request.for_fork?
     end
 

doc/ci/merge_request_pipelines/pipelines_for_merged_results/index.md

@@ -93,7 +93,6 @@ canceled.
 Can be caused by some disabled feature flags. Please make sure that
 the following feature flags are enabled on your GitLab instance:
 
-- `:ci_use_merge_request_ref`
 - `:merge_ref_auto_sync`
 
 To check and set these feature flag values, please ask an administrator to:
@@ -107,14 +106,12 @@ To check and set these feature flag values, please ask an administrator to:
 1. Check if the flags are enabled or not:
 
    ```ruby
-   Feature.enabled?(:ci_use_merge_request_ref)
    Feature.enabled?(:merge_ref_auto_sync)
    ```
 
 1. If needed, enable the feature flags:
 
    ```ruby
-   Feature.enable(:ci_use_merge_request_ref)
    Feature.enable(:merge_ref_auto_sync)
    ```
 

ee/spec/services/ee/merge_requests/create_pipeline_service_spec.rb

@@ -76,14 +76,6 @@ describe MergeRequests::CreatePipelineService, :clean_gitlab_redis_shared_state
       it_behaves_like 'detached merge request pipeline'
     end
 
-    context 'when ci_use_merge_request_ref feature flag is disabled' do
-      before do
-        stub_feature_flags(ci_use_merge_request_ref: false)
-      end
-
-      it_behaves_like 'detached merge request pipeline'
-    end
-
     context 'when merge request is submitted from fork' do
       let(:source_project) { fork_project(project, nil, repository: true) }
 

spec/services/merge_requests/create_service_spec.rb

@@ -224,19 +224,6 @@ describe MergeRequests::CreateService, :clean_gitlab_redis_shared_state do
             end
           end
 
-          context 'when ci_use_merge_request_ref feature flag is false' do
-            before do
-              stub_feature_flags(ci_use_merge_request_ref: false)
-            end
-
-            it 'create legacy detached merge request pipeline for non-fork merge request' do
-              merge_request.reload
-
-              expect(merge_request.actual_head_pipeline)
-                .to be_legacy_detached_merge_request_pipeline
-            end
-          end
-
           context 'when there are no commits between source branch and target branch' do
             let(:opts) do
               {

spec/services/merge_requests/refresh_service_spec.rb

@@ -209,19 +209,6 @@ describe MergeRequests::RefreshService do
           end
         end
 
-        context 'when ci_use_merge_request_ref feature flag is false' do
-          before do
-            stub_feature_flags(ci_use_merge_request_ref: false)
-          end
-
-          it 'create legacy detached merge request pipeline for non-fork merge request' do
-            subject
-
-            expect(@merge_request.pipelines_for_merge_request.first)
-              .to be_legacy_detached_merge_request_pipeline
-          end
-        end
-
         context "when branch pipeline was created before a detaced merge request pipeline has been created" do
           before do
             create(:ci_pipeline, project: @merge_request.source_project,