GUI-1414 removed S3 upload warning

removed upload warning

https://eucalyptus.atlassian.net/browse/GUI-1414
@dkavanagh: I'm not sure if we should allow this config, since the gunicorn docs at http://gunicorn-docs.readthedocs.org/en/19.1.1/settings.html?highlight=tmp_upload_dir#tmp-upload-dir clearly state that the tmp_upload_dir option"... may disappear in the near future."