Remove redundant comment and cop disable

After https://gitlab.com/gitlab-org/gitlab/merge_requests/18002 was
merged, we could use comments on the opening block line, thus the
commentary in `fast_hash_serializer.rb` is no longer relevant.
Also, removing unnecessary cop disable in `base_exporter.rb`.

lib/gitlab/import_export/fast_hash_serializer.rb

@@ -135,10 +135,7 @@ module Gitlab
 
         data = []
 
-        # rubocop:disable Cop/InBatches
-        # If we put `rubocop:disable` inline after `do |batch|`,
-        # `Cop/LineBreakAroundConditionalBlock` will fail
-        record.in_batches(of: @batch_size) do |batch|
+        record.in_batches(of: @batch_size) do |batch| # rubocop:disable Cop/InBatches
           if Feature.enabled?(:export_fast_serialize_with_raw_json, default_enabled: true)
             data.append(JSONBatchRelation.new(batch, options, preloads[key]).tap(&:raw_json))
           else
@@ -146,7 +143,6 @@ module Gitlab
             data += batch.as_json(options)
           end
         end
-        # rubocop:enable Cop/InBatches
 
         data
       end

lib/gitlab/metrics/exporter/base_exporter.rb

@@ -36,10 +36,11 @@ module Gitlab
         end
 
         def stop_working
-          if server # rubocop:disable Cop/LineBreakAroundConditionalBlock
+          if server
             server.shutdown
             server.listeners.each(&:close)
           end
+
           @server = nil
         end