Remove the codequality_mr_diff feature flag

Remove YAML definition
Remove helper from features
Remove references to helper from merge_request and pipeline
Remove feature flag test cases from specs
Remove instructions to disable the flag from the docs

Changelog: other
EE: true

app/models/ci/pipeline.rb

@@ -1026,8 +1026,6 @@ module Ci
     end
 
     def can_generate_codequality_reports?
-      return false unless ::Gitlab::Ci::Features.display_quality_on_mr_diff?(project)
-
       has_reports?(Ci::JobArtifact.codequality_reports)
     end
 

app/models/merge_request.rb

@@ -1556,8 +1556,6 @@ class MergeRequest < ApplicationRecord
   end
 
   def has_codequality_mr_diff_report?
-    return false unless ::Gitlab::Ci::Features.display_quality_on_mr_diff?(project)
-
     actual_head_pipeline&.has_codequality_mr_diff_report?
   end
 

config/feature_flags/development/codequality_mr_diff.yml

----
-name: codequality_mr_diff
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/47938
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/284140
-milestone: '13.7'
-type: development
-group: group::testing
-default_enabled: false

doc/user/project/merge_requests/code_quality.md

@@ -59,6 +59,7 @@ See also the Code Climate list of [Supported Languages for Maintainability](http
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/267612) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 13.11.
 > - [Deployed behind a feature flag](../../../user/feature_flags.md), disabled by default.
 > - [Enabled by default](https://gitlab.com/gitlab-org/gitlab/-/issues/284140) in GitLab 13.12.
+> - [Feature flag removed](https://gitlab.com/gitlab-org/gitlab/-/issues/284140) in GitLab 14.0.
 > - [Feature enhanced](https://gitlab.com/gitlab-org/gitlab/-/issues/2526) in GitLab 14.0.
 
 Changes to files in merge requests can cause Code Quality to fall if merged. In these cases,

lib/gitlab/ci/features.rb

@@ -22,10 +22,6 @@ module Gitlab
         ::Feature.enabled?(:ci_trace_log_invalid_chunks, project, type: :ops, default_enabled: false)
       end
 
-      def self.display_quality_on_mr_diff?(project)
-        ::Feature.enabled?(:codequality_mr_diff, project, default_enabled: :yaml)
-      end
-
       def self.gldropdown_tags_enabled?
         ::Feature.enabled?(:gldropdown_tags, default_enabled: :yaml)
       end

spec/models/ci/pipeline_spec.rb

@@ -3811,16 +3811,6 @@ RSpec.describe Ci::Pipeline, :mailer, factory_default: :keep do
         it 'can generate a codequality report' do
           expect(subject).to be_truthy
         end
-
-        context 'when feature is disabled' do
-          before do
-            stub_feature_flags(codequality_mr_diff: false)
-          end
-
-          it 'can not generate a codequality report' do
-            expect(subject).to be_falsey
-          end
-        end
       end
     end
 

spec/models/merge_request_spec.rb

@@ -2083,14 +2083,6 @@ RSpec.describe MergeRequest, factory_default: :keep do
       let(:merge_request) { create(:merge_request, :with_codequality_mr_diff_reports) }
 
       it { is_expected.to be_truthy }
-
-      context 'when feature flag is disabled' do
-        before do
-          stub_feature_flags(codequality_mr_diff: false)
-        end
-
-        it { is_expected.to be_falsey }
-      end
     end
 
     context 'when head pipeline does not have codeqquality mr diff report' do