Remove feature flag optimize_merge_request_parser

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/331893

Merge request parser optimization improves the rendering time. Keep
the new version of the code.

Changelog: changed

config/feature_flags/development/optimize_merge_request_parser.yml

----
-name: optimize_merge_request_parser
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/62490/
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/331893
-milestone: '14.0'
-type: development
-group: group::source code
-default_enabled: false

lib/banzai/reference_parser/merge_request_parser.rb

@@ -8,8 +8,6 @@ module Banzai
       self.reference_type = :merge_request
 
       def nodes_visible_to_user(user, nodes)
-        return super if Feature.disabled?(:optimize_merge_request_parser, user, default_enabled: :yaml)
-
         merge_request_nodes = nodes.select { |node| node.has_attribute?(self.class.data_attribute) }
         records = projects_for_nodes(merge_request_nodes)
 

spec/lib/banzai/reference_parser/merge_request_parser_spec.rb

@@ -23,14 +23,6 @@ RSpec.describe Banzai::ReferenceParser::MergeRequestParser do
       end
 
       it_behaves_like "referenced feature visibility", "merge_requests"
-
-      context 'when optimize_merge_request_parser feature flag is off' do
-        before do
-          stub_feature_flags(optimize_merge_request_parser: false)
-        end
-
-        it_behaves_like "referenced feature visibility", "merge_requests"
-      end
     end
   end