Investigate removing tarball crawling from the sitemap.

https://github.com/haskell/hackage-server/blob/866279e7f8e633c2d63f957b51d7e6836b91aced/src/Distribution/Server/Features/Sitemap.hs#L276

This was added in gsoc a few years ago as art of sitemap improvements, but may be too costly when we do it all at once over a network drive. Likely matters little for google or other crawlers, may as well disable and see if it helps performance, since this seems to be a midnight job that corresponds to heavy load.