Remove Akamai-related code

Revert 9b54b2ca20f6996bad76a4901715c6e0a881bd9b

This removes the logic that prevents adding cache buster value to the URL if the image is less than 10 minutes old. Images with URLs without cb value are cached only for 5 minutes.

Cleanup:

* remove ``$wgAkamaiGlobalVersion``
* remove ``$wgAkamaiLocalVersion``

@prein / @michalroszka / @ljagiello