Brandon, I had a "monday morning quarterback" moment (don't worry, it's not too bad)

The key we chose is "WMF-Last-Access" and it seems to me that's using a lot of unnecessary network bandwidth with its verbosity.  We could come up with something shorter (I cc-ed Analytics in case anyone has an opinion) and save our network.  My proposal: simply "last"

For those unfamiliar, we're talking about this change: https://gerrit.wikimedia.org/r/#/c/196009/14/templates/varnish/last-access.inc.vcl.erb to this header: https://wikitech.wikimedia.org/wiki/X-Analytics