Remove Kramdown patch and update to v2.3.1 gem

As of https://gitlab.com/gitlab-org/gitlab/-/merge_requests/56750,
Markdown should no longer be rendered through Kramdown for Wiki
pages. The monkey patch can be removed with Kramdown v2.3.1.

Diff:
https://my.diffend.io/gems/kramdown/2.3.0/2.3.1

Gemfile

@@ -150,7 +150,7 @@ gem 'deckar01-task_list', '2.3.1'
 gem 'gitlab-markup', '~> 1.7.1'
 gem 'github-markup', '~> 1.7.0', require: 'github/markup'
 gem 'commonmarker', '~> 0.21'
-gem 'kramdown', '~> 2.3.0'
+gem 'kramdown', '~> 2.3.1'
 gem 'RedCloth', '~> 4.3.2'
 gem 'rdoc', '~> 6.1.2'
 gem 'org-ruby', '~> 0.9.12'

Gemfile.lock

@@ -669,7 +669,7 @@ GEM
     kgio (2.11.3)
     knapsack (1.17.0)
       rake
-    kramdown (2.3.0)
+    kramdown (2.3.1)
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
@@ -1471,7 +1471,7 @@ DEPENDENCIES
   jwt (~> 2.1.0)
   kaminari (~> 1.0)
   knapsack (~> 1.17)
-  kramdown (~> 2.3.0)
+  kramdown (~> 2.3.1)
   kubeclient (~> 4.9.1)
   lefthook (~> 0.7)
   letter_opener_web (~> 1.3.4)

changelogs/unreleased/sh-remove-kramdown-patch.yml

+---
+title: Remove Kramdown patch and update to v2.3.1 gem
+merge_request: 56917
+author:
+type: fixed

config/initializers/kramdown_patch.rb

-# frozen_string_literal: true
-#
-# This pulls in https://github.com/gettalong/kramdown/pull/708 for kramdown v2.3.0.
-# Remove this file when that pull request is merged and released.
-require 'kramdown/converter'
-require 'kramdown/converter/syntax_highlighter/rouge'
-
-module Kramdown::Converter::SyntaxHighlighter
-  module Rouge
-    def self.formatter_class(opts = {})
-      case formatter = opts[:formatter]
-      when Class
-        formatter
-      when /\A[[:upper:]][[:alnum:]_]*\z/
-        ::Rouge::Formatters.const_get(formatter, false)
-      else
-        # Available in Rouge 2.0 or later
-        ::Rouge::Formatters::HTMLLegacy
-      end
-    rescue NameError
-      # Fallback to Rouge 1.x
-      ::Rouge::Formatters::HTML
-    end
-  end
-end

spec/initializers/kramdown_patch_spec.rb → spec/lib/kramdown/kramdown_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-RSpec.describe 'Kramdown patch for syntax highlighting formatters' do
+RSpec.describe 'Ensure kramdown detects invalid syntax highlighting formatters' do
   subject { Kramdown::Document.new(options + "\n" + code).to_html }
 
   let(:code) do