Optimize Nokogiri search for post-processing pipeline

* Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/271242
* FF issue: https://gitlab.com/gitlab-org/gitlab/-/issues/328696

Enable Nokogiri optimization by default

Changelog: performance

config/feature_flags/development/optimize_linkable_attributes.yml

----
-name: optimize_linkable_attributes
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/59983
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/328696
-milestone: '13.12'
-type: development
-group: group::source code
-default_enabled: false

lib/banzai/filter/base_relative_link_filter.rb

@@ -10,18 +10,12 @@ module Banzai
       protected
 
       def linkable_attributes
-        if Feature.enabled?(:optimize_linkable_attributes, project, default_enabled: :yaml)
-          # Nokorigi Nodeset#search performs badly for documents with many nodes
-          #
-          # Here we store fetched attributes in the shared variable "result"
-          # This variable is passed through the chain of filters and can be
-          # accessed by them
-          result[:linkable_attributes] ||= fetch_linkable_attributes
-        else
-          strong_memoize(:linkable_attributes) do
-            fetch_linkable_attributes
-          end
-        end
+        # Nokorigi Nodeset#search performs badly for documents with many nodes
+        #
+        # Here we store fetched attributes in the shared variable "result"
+        # This variable is passed through the chain of filters and can be
+        # accessed by them
+        result[:linkable_attributes] ||= fetch_linkable_attributes
       end
 
       def relative_url_root

lib/banzai/filter/upload_link_filter.rb

@@ -15,16 +15,10 @@ module Banzai
       def call
         return doc if context[:system_note]
 
-        if Feature.enabled?(:optimize_linkable_attributes, project, default_enabled: :yaml)
-          # We exclude processed upload links from the linkable attributes to
-          # prevent further modifications by RepositoryLinkFilter
-          linkable_attributes.reject! do |attr|
-            process_link_to_upload_attr(attr)
-          end
-        else
-          linkable_attributes.each do |attr|
-            process_link_to_upload_attr(attr)
-          end
+        # We exclude processed upload links from the linkable attributes to
+        # prevent further modifications by RepositoryLinkFilter
+        linkable_attributes.reject! do |attr|
+          process_link_to_upload_attr(attr)
         end
 
         doc

spec/lib/banzai/pipeline/post_process_pipeline_spec.rb

@@ -42,17 +42,5 @@ RSpec.describe Banzai::Pipeline::PostProcessPipeline do
 
       subject
     end
-
-    context 'when "optimize_linkable_attributes" is disabled' do
-      before do
-        stub_feature_flags(optimize_linkable_attributes: false)
-      end
-
-      it 'searches for attributes twice' do
-        expect(doc).to receive(:search).twice.and_call_original
-
-        subject
-      end
-    end
   end
 end