Remove limited_diff_highlighting feature flag

config/feature_flags/development/limited_diff_highlighting.yml

----
-name: limited_diff_highlighting
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/53768
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/323566
-milestone: '13.12'
-type: development
-group: group::source code
-default_enabled: true

lib/gitlab/diff/highlight.rb

@@ -159,7 +159,6 @@ module Gitlab
       end
 
       def blobs_too_large?
-        return false unless Feature.enabled?(:limited_diff_highlighting, project, default_enabled: :yaml)
         return true if Gitlab::Highlight.too_large?(diff_file.old_blob&.size)
 
         Gitlab::Highlight.too_large?(diff_file.new_blob&.size)

spec/lib/gitlab/diff/highlight_spec.rb

@@ -151,20 +151,6 @@ RSpec.describe Gitlab::Diff::Highlight do
         expect(subject[2].rich_text).to eq(%Q{ <span id="LC7" class="line" lang="">  def popen(cmd, path=nil)</span>\n})
         expect(subject[2].rich_text).to be_html_safe
       end
-
-      context 'when limited_diff_highlighting is disabled' do
-        before do
-          stub_feature_flags(limited_diff_highlighting: false)
-          stub_feature_flags(diff_line_syntax_highlighting: false)
-        end
-
-        it 'blobs are highlighted as plain text with loading all data' do
-          expect(diff_file.blob).to receive(:load_all_data!).twice
-
-          code = %Q{ <span id="LC7" class="line" lang="">  def popen(cmd, path=nil)</span>\n}
-          expect(subject[2].rich_text).to eq(code)
-        end
-      end
     end
   end
 end