Move merge-request merge_pipeline to cached_widget

Remove merge_request_cached_merge_pipeline_serializer FF

The FF has been enabled by default for some time
We can remove it

Changelog: performance

app/serializers/merge_request_poll_cached_widget_entity.rb

@@ -50,11 +50,7 @@ class MergeRequestPollCachedWidgetEntity < IssuableEntity
     MergeRequests::PipelineEntity.represent(merge_request.actual_head_pipeline, options)
   end
 
-  expose :merge_pipeline, if: ->(mr, _) {
-    Feature.enabled?(:merge_request_cached_merge_pipeline_serializer, mr.project, default_enabled: :yaml) &&
-      mr.merged? &&
-      can?(request.current_user, :read_pipeline, mr.target_project)
-  } do |merge_request, options|
+  expose :merge_pipeline, if: ->(mr, _) { mr.merged? && can?(request.current_user, :read_pipeline, mr.target_project) } do |merge_request, options|
     MergeRequests::PipelineEntity.represent(merge_request.merge_pipeline, options)
   end
 

app/serializers/merge_request_poll_widget_entity.rb

@@ -19,14 +19,6 @@ class MergeRequestPollWidgetEntity < Grape::Entity
   # User entities
   expose :merge_user, using: UserEntity
 
-  expose :merge_pipeline, if: ->(mr, _) {
-    Feature.disabled?(:merge_request_cached_merge_pipeline_serializer, mr.project, default_enabled: :yaml) &&
-      mr.merged? &&
-      can?(request.current_user, :read_pipeline, mr.target_project)
-  } do |merge_request, options|
-    MergeRequests::PipelineEntity.represent(merge_request.merge_pipeline, options)
-  end
-
   expose :default_merge_commit_message
 
   expose :mergeable do |merge_request, options|

config/feature_flags/development/merge_request_cached_merge_pipeline_serializer.yml

----
-name: merge_request_cached_merge_pipeline_serializer
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57827
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/326317
-milestone: '13.11'
-type: development
-group: group::source code
-default_enabled: false

spec/serializers/merge_request_poll_cached_widget_entity_spec.rb

@@ -302,16 +302,6 @@ RSpec.describe MergeRequestPollCachedWidgetEntity do
           expect(subject[:merge_pipeline]).to be_nil
         end
       end
-
-      context 'when merge_request_cached_merge_pipeline_serializer is disabled' do
-        before do
-          stub_feature_flags(merge_request_cached_merge_pipeline_serializer: false)
-        end
-
-        it 'returns nil' do
-          expect(subject[:merge_pipeline]).to be_nil
-        end
-      end
     end
   end
 

spec/serializers/merge_request_poll_widget_entity_spec.rb

@@ -22,54 +22,6 @@ RSpec.describe MergeRequestPollWidgetEntity do
       .to eq(resource.default_merge_commit_message(include_description: true))
   end
 
-  describe 'merge_pipeline' do
-    before do
-      stub_feature_flags(merge_request_cached_merge_pipeline_serializer: false)
-    end
-
-    it 'returns nil' do
-      expect(subject[:merge_pipeline]).to be_nil
-    end
-
-    context 'when is merged' do
-      let_it_be(:resource) { create(:merged_merge_request, source_project: project, merge_commit_sha: project.commit.id) }
-      let_it_be(:pipeline) { create(:ci_empty_pipeline, project: project, ref: resource.target_branch, sha: resource.merge_commit_sha) }
-
-      before do
-        project.add_maintainer(user)
-      end
-
-      context 'when user cannot read pipelines on target project' do
-        before do
-          project.team.truncate
-        end
-
-        it 'returns nil' do
-          expect(subject[:merge_pipeline]).to be_nil
-        end
-      end
-
-      it 'returns merge_pipeline' do
-        pipeline_payload =
-          MergeRequests::PipelineEntity
-            .represent(pipeline, request: request)
-            .as_json
-
-        expect(subject[:merge_pipeline]).to eq(pipeline_payload)
-      end
-
-      context 'when merge_request_cached_merge_pipeline_serializer is enabled' do
-        before do
-          stub_feature_flags(merge_request_cached_merge_pipeline_serializer: true)
-        end
-
-        it 'returns nil' do
-          expect(subject[:merge_pipeline]).to be_nil
-        end
-      end
-    end
-  end
-
   describe 'new_blob_path' do
     context 'when user can push to project' do
       it 'returns path' do