Remove load_balancing_for_export_workers ff

config/feature_flags/development/load_balancing_for_export_workers.yml

----
-name: load_balancing_for_export_workers
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/68153
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/338615
-milestone: '14.2'
-type: development
-group: group::import
-default_enabled: false

lib/gitlab/import_export/json/streaming_serializer.rb

@@ -166,8 +166,6 @@ module Gitlab
         end
 
         def read_from_replica_if_available(&block)
-          return yield unless ::Feature.enabled?(:load_balancing_for_export_workers, type: :development, default_enabled: :yaml)
-
           ::Gitlab::Database::LoadBalancing::Session.current.use_replicas_for_read_queries(&block)
         end
       end

spec/lib/gitlab/import_export/json/streaming_serializer_spec.rb

@@ -158,26 +158,10 @@ RSpec.describe Gitlab::ImportExport::Json::StreamingSerializer do
     end
 
     describe 'load balancing' do
-      context 'when feature flag load_balancing_for_export_workers is enabled' do
-        before do
-          stub_feature_flags(load_balancing_for_export_workers: true)
-        end
-
-        it 'reads from replica' do
-          expect(Gitlab::Database::LoadBalancing::Session.current).to receive(:use_replicas_for_read_queries).and_call_original
-
-          subject.execute
-        end
-      end
+      it 'reads from replica' do
+        expect(Gitlab::Database::LoadBalancing::Session.current).to receive(:use_replicas_for_read_queries).and_call_original
 
-      context 'when feature flag load_balancing_for_export_workers is disabled' do
-        it 'reads from primary' do
-          stub_feature_flags(load_balancing_for_export_workers: false)
-
-          expect(Gitlab::Database::LoadBalancing::Session.current).not_to receive(:use_replicas_for_read_queries)
-
-          subject.execute
-        end
+        subject.execute
       end
     end
   end