GeoIP cookie: expand deployment from Labs to production

Enabled on Labs in change I7ea70060 (14 March). The bug whereby cookies could
be clobbered if multiple Set-Cookie headers were present on the response has
been fixed, and no further issues have been noted, so I think this is ready for
prime-time.

Change-Id: I2d0a270d6b15e8deee6210c151ea48bc75160391