BAC-1241: remove X-Pass-Expires from ResourceLoader
Remove Akamai-related code

* revert 9b54b2ca20f6996bad76a4901715c6e0a881bd9b
* remove $wgAkamaiGlobalVersion
* remove $wgAkamaiLocalVersion
BAC-1312: don't purge avatars

They already have cb in URL
Merge pull request #2811 from Wikia/release-210-varnish

Varnish backports to release-210