text: Title: Clean up test_download_gzip_response
  Body: The test is currently skipped due to some Python-2-only code. We should instead remove that code.
  
  https://github.com/scrapy/scrapy/blob/42b3a3a23b328741f1720953235a62cba120ae7b/tests/test_downloader_handlers.py#L729-L754