Remove export_reduce_relation_batch_size feature flag

Changelog: changed

config/feature_flags/development/export_reduce_relation_batch_size.yml

----
-name: export_reduce_relation_batch_size
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/34057
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/282245
-milestone: '13.1'
-type: development
-group: group::import
-default_enabled: false

lib/gitlab/import_export/json/streaming_serializer.rb

@@ -6,16 +6,11 @@ module Gitlab
       class StreamingSerializer
         include Gitlab::ImportExport::CommandLineUtil
 
-        BATCH_SIZE = 100
-        SMALLER_BATCH_SIZE = 2
+        BATCH_SIZE = 2
 
         def self.batch_size(exportable)
-          if Feature.enabled?(:export_reduce_relation_batch_size, exportable)
-            SMALLER_BATCH_SIZE
-          else
           BATCH_SIZE
         end
-        end
 
         class Raw < String
           def to_json(*_args)

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

@@ -183,24 +183,8 @@ RSpec.describe Gitlab::ImportExport::Json::StreamingSerializer do
   end
 
   describe '.batch_size' do
-    context 'when export_reduce_relation_batch_size feature flag is enabled' do
-      before do
-        stub_feature_flags(export_reduce_relation_batch_size: true)
-      end
-
-      it 'returns 20' do
-        expect(described_class.batch_size(exportable)).to eq(described_class::SMALLER_BATCH_SIZE)
-      end
-    end
-
-    context 'when export_reduce_relation_batch_size feature flag is disabled' do
-      before do
-        stub_feature_flags(export_reduce_relation_batch_size: false)
-      end
-
     it 'returns default batch size' do
       expect(described_class.batch_size(exportable)).to eq(described_class::BATCH_SIZE)
     end
   end
-  end
 end

spec/lib/gitlab/import_export/legacy_relation_tree_saver_spec.rb

@@ -8,13 +8,12 @@ RSpec.describe Gitlab::ImportExport::LegacyRelationTreeSaver do
   let(:tree) { {} }
 
   describe '#serialize' do
-    shared_examples 'FastHashSerializer with batch size' do |batch_size|
     let(:serializer) { instance_double(Gitlab::ImportExport::FastHashSerializer) }
 
     it 'uses FastHashSerializer' do
       expect(Gitlab::ImportExport::FastHashSerializer)
         .to receive(:new)
-          .with(exportable, tree, batch_size: batch_size)
+        .with(exportable, tree, batch_size: Gitlab::ImportExport::Json::StreamingSerializer::BATCH_SIZE)
         .and_return(serializer)
 
       expect(serializer).to receive(:execute)
@@ -22,21 +21,4 @@ RSpec.describe Gitlab::ImportExport::LegacyRelationTreeSaver do
       relation_tree_saver.serialize(exportable, tree)
     end
   end
-
-    context 'when export_reduce_relation_batch_size feature flag is enabled' do
-      before do
-        stub_feature_flags(export_reduce_relation_batch_size: true)
-      end
-
-      include_examples 'FastHashSerializer with batch size', Gitlab::ImportExport::Json::StreamingSerializer::SMALLER_BATCH_SIZE
-    end
-
-    context 'when export_reduce_relation_batch_size feature flag is disabled' do
-      before do
-        stub_feature_flags(export_reduce_relation_batch_size: false)
-      end
-
-      include_examples 'FastHashSerializer with batch size', Gitlab::ImportExport::Json::StreamingSerializer::BATCH_SIZE
-    end
-  end
 end